diff --git a/src/guf_str.h b/src/guf_str.h
index 8365b0a..ffda8fb 100644
--- a/src/guf_str.h
+++ b/src/guf_str.h
@@ -60,8 +60,8 @@ typedef struct guf_str {
 
 #ifdef __cplusplus
     // Standard C++ does not have compound literals like C99...
-    #define GUF_CSTR_TO_VIEW_CPP(CSTR) guf_str_view{.str = (CSTR), .len = (ptrdiff_t)strlen(CSTR)}
-    #define GUF_CSTR_LIT_TO_VIEW_CPP(CSTR) guf_str_view{.str = (CSTR), .len = (ptrdiff_t)sizeof(CSTR) - 1}
+    #define GUF_CSTR_TO_VIEW_CPP(CSTR) guf_str_view {.str = (CSTR), .len = (ptrdiff_t)strlen(CSTR)}
+    #define GUF_CSTR_LIT_TO_VIEW_CPP(CSTR) guf_str_view {.str = (CSTR), .len = (ptrdiff_t)sizeof(CSTR) - 1}
 
     #define GUF_STR_UNINITIALISED_CPP guf_str{.allocator = NULL, .data.shrt.size = 0, .data.shrt.c_str[0] = '\0'}
 #endif
@@ -84,10 +84,9 @@ GUF_STR_KWRDS guf_str_view guf_str_view_trim_left_ascii(guf_str_view sv);
 GUF_STR_KWRDS guf_str_view guf_str_next_tok(guf_str_view *input, const guf_str_view *delims, ptrdiff_t num_delims, const guf_str_view *preserved_delims, ptrdiff_t num_preserved_delims);
 
 // guf_str:
-
-// DONE:
 GUF_STR_KWRDS guf_str *guf_str_try_init(guf_str *str, guf_str_view str_view, guf_allocator *alloc, guf_err *err);
 GUF_STR_KWRDS guf_str *guf_str_init(guf_str *str, guf_str_view str_view, guf_allocator *alloc);
+GUF_STR_KWRDS guf_str *guf_str_init_empty(guf_str *str, guf_allocator *alloc);
 
 GUF_STR_KWRDS guf_str *guf_str_try_init_from_cstr(guf_str *str, const char* c_str, guf_allocator *alloc, guf_err *err);
 GUF_STR_KWRDS guf_str *guf_str_init_from_cstr(guf_str *str, const char* c_str, guf_allocator *alloc);
@@ -98,11 +97,24 @@ GUF_STR_KWRDS guf_str guf_str_new(guf_str_view str_view, guf_allocator *alloc);
 GUF_STR_KWRDS void guf_str_free(guf_str *str, void *ctx);
 GUF_STR_KWRDS guf_str *guf_str_copy(guf_str *dst, const guf_str *src, void *ctx);
 GUF_STR_KWRDS guf_str *guf_str_move(guf_str *dst, guf_str *src, void *ctx);
-
 GUF_STR_KWRDS bool guf_str_equal(const guf_str *a, const guf_str *b);
 GUF_STR_KWRDS int guf_str_cmp(const guf_str *a, const guf_str *b);
 
-// DONE:
+// Reserve at least min_capacity characters (excluding the null-terminator) (try to double the current capacity first; if that's not at least min_capacity, set the new capacity to min_capacity instead).
+GUF_STR_KWRDS guf_str *guf_str_try_reserve(guf_str *str, ptrdiff_t min_capacity, guf_err *err); 
+GUF_STR_KWRDS guf_str *guf_str_reserve(guf_str *str, ptrdiff_t min_capacity); 
+// Shrink the capacity of the string so it does not waste space (short-string-optimisation will be applied if the new capacity <= GUF_STR_SSO_BUF_CAP)
+GUF_STR_KWRDS guf_str *guf_str_try_shrink_to_fit(guf_str *str, guf_err *err);
+GUF_STR_KWRDS guf_str *guf_str_shrink_to_fit(guf_str *str);
+
+// Set the contents of str to the given string view (mutating str) -> return the mutated str
+GUF_STR_KWRDS guf_str *guf_str_try_set(guf_str *str, guf_str_view str_view, guf_err *err);
+GUF_STR_KWRDS guf_str *guf_str_set(guf_str *str, guf_str_view str_view);
+
+// Return a view of the string.
+GUF_STR_KWRDS guf_str_view guf_str_to_view(const guf_str *str);
+
+// Return a non-const pointer to the character at the specified index of str (if possible)
 GUF_STR_KWRDS char *guf_str_try_at(guf_str *str, ptrdiff_t idx, guf_err *err);
 GUF_STR_KWRDS char *guf_str_at(guf_str *str, ptrdiff_t idx);
 GUF_STR_KWRDS char *guf_str_try_back(guf_str *str, guf_err *err);
@@ -110,6 +122,7 @@ GUF_STR_KWRDS char *guf_str_back(guf_str *str);
 GUF_STR_KWRDS char *guf_str_try_front(guf_str *str, guf_err *err);
 GUF_STR_KWRDS char *guf_str_front(guf_str *str);
 
+// Return a copy of the char at the specified index of str (if possible)
 GUF_STR_KWRDS char guf_str_try_at_cpy(const guf_str *str, ptrdiff_t idx, guf_err *err);
 GUF_STR_KWRDS char guf_str_at_cpy(const guf_str *str, ptrdiff_t idx);
 GUF_STR_KWRDS char guf_str_try_back_cpy(const guf_str *str, guf_err *err);
@@ -117,45 +130,42 @@ GUF_STR_KWRDS char guf_str_back_cpy(const guf_str *str);
 GUF_STR_KWRDS char guf_str_try_front_cpy(const guf_str *str, guf_err *err);
 GUF_STR_KWRDS char guf_str_front_cpy(const guf_str *str);
 
-// DONE:
-// Make substring in-place (constant time if pos == 0, otherwise copying count chars to the beginning of the str, i.e. linear time)
+/*
+    Turn str into the substring in range [pos, pos + count) (mutating str) -> return the mutated str
+    (Constant time if pos == 0, otherwise copying count chars to the beginning of the str, i.e. linear time.)
+    NOTE: To make a substring-copy (instead of mutating str), create a guf_str_view of str and use guf_str_view_substr
+*/
 GUF_STR_KWRDS guf_str *guf_str_try_substr(guf_str *str, ptrdiff_t pos, ptrdiff_t count, guf_err *err);
 GUF_STR_KWRDS guf_str *guf_str_substr(guf_str *str, ptrdiff_t pos, ptrdiff_t count);
 
-// TODO:
+// Remove the last character from str if possible (mutating str) -> return the popped char
+GUF_STR_KWRDS char guf_str_try_pop_back(guf_str *str, guf_err *err); 
 GUF_STR_KWRDS char guf_str_pop_back(guf_str *str); 
-GUF_STR_KWRDS char guf_str_pop_front(guf_str *str);
 
-// DONE: 
+// Append a char to str (n times; times must be >= 0) (mutating str) -> return the mutated str
 GUF_STR_KWRDS guf_str *guf_str_try_append_char(guf_str *str, char c, ptrdiff_t times, guf_err *err);
 GUF_STR_KWRDS guf_str *guf_str_append_char(guf_str *str, char c, ptrdiff_t times);
 GUF_STR_KWRDS guf_str *guf_str_try_append_one_char(guf_str *str, char c, guf_err *err);
 GUF_STR_KWRDS guf_str *guf_str_append_one_char(guf_str *str, char c);
 
+// Append str_view to str (mutating str) -> return the mutated str
 GUF_STR_KWRDS guf_str *guf_str_try_append(guf_str *str, guf_str_view sv, guf_err *err);
 GUF_STR_KWRDS guf_str *guf_str_append(guf_str *str, guf_str_view sv);
 
-GUF_STR_KWRDS guf_str *guf_str_try_append_cstr(guf_str *str, const char *c_str, guf_err *err);
-GUF_STR_KWRDS guf_str *guf_str_append_cstr(guf_str *str, const char *c_str);
-
-// DONE:
-GUF_STR_KWRDS guf_str *guf_str_try_reserve(guf_str *str, ptrdiff_t min_capacity, guf_err *err); 
-GUF_STR_KWRDS guf_str *guf_str_reserve(guf_str *str, ptrdiff_t min_capacity); 
-
-// TODO:
-GUF_STR_KWRDS guf_str *guf_str_try_shrink_to_fit(guf_str *str, guf_err *err);
-GUF_STR_KWRDS guf_str *guf_str_shrink_to_fit(guf_str *str);
-
-// DONE: 
+// Return a pointer to the null-terminated char array representing the string (works like std::string::c_str in C++)
 GUF_STR_KWRDS const char *guf_str_const_cstr(const guf_str *str);
 GUF_STR_KWRDS char *guf_str_try_get_cstr(guf_str *str, guf_err *err); // Error if str is readonly.
 GUF_STR_KWRDS char *guf_str_cstr(guf_str *str); // Panics if str is readonly.
 
-GUF_STR_KWRDS ptrdiff_t guf_str_len(const guf_str *str);      // The length (in chars) without the final zero-terminator. 
-GUF_STR_KWRDS ptrdiff_t guf_str_capacity(const guf_str *str); // The capacity (in chars) without the final zero-terminator. 
+// Return the length/capacity (in chars) *without* the final null-terminator.
+GUF_STR_KWRDS ptrdiff_t guf_str_len(const guf_str *str);  
+GUF_STR_KWRDS ptrdiff_t guf_str_capacity(const guf_str *str); 
 
+// Return true if the char data of the string lives directly within the guf_str itself (short-string optimisation) instead of in a separate dynamic allocation
 GUF_STR_KWRDS bool guf_str_is_short(const guf_str *str);
+// Return true if the string is in readonly ("view") mode, i.e. can't be modified, copied etc. which is useful for guf_dict so we don't have to use guf_str_view but can use guf_str (by passing a read-only guf_str) for the lookup functions.
 GUF_STR_KWRDS bool guf_str_is_readonly(const guf_str *str);
+// Return true if the string's data does not violate its invariants (useful for debugging, should never be false after initialising if there are not bugs in guf_str). 
 GUF_STR_KWRDS bool guf_str_is_valid(const guf_str *str);
 
 GUF_STR_KWRDS guf_str guf_str_new_uninitialised(void);
@@ -198,7 +208,7 @@ GUF_STR_KWRDS bool guf_str_is_uninit(const guf_str *str);
     }
     static inline void guf_str_set_shrt_size_(guf_str *str, unsigned char size_with_null)
     {
-        GUF_ASSERT(size_with_null < GUF_STR_SSO_BUF_CAP && size_with_null < 0x80);
+        GUF_ASSERT(size_with_null <= GUF_STR_SSO_BUF_CAP && size_with_null < 0x80); // TODO: was < SSO_CAP, should be <= SSO_CAP?
         str->data.shrt.size = (unsigned char)(size_with_null << 1);
     }
 #elif defined(GUF_PLATFORM_BIG_ENDIAN)
@@ -214,7 +224,7 @@ GUF_STR_KWRDS bool guf_str_is_uninit(const guf_str *str);
     }
     static inline void guf_str_set_shrt_size_(guf_str *str, unsigned char size_with_null)
     {
-        GUF_ASSERT(size_with_null < GUF_STR_SSO_BUF_CAP && size_with_null < 0x80);
+        GUF_ASSERT(size_with_null <= GUF_STR_SSO_BUF_CAP && size_with_null < 0x80); // TODO: was < SSO_CAP, should be <=
         str->data.shrt.size = size_with_null;
     }
 #else
@@ -328,20 +338,25 @@ GUF_STR_KWRDS bool guf_str_is_valid(const guf_str *str)
         return size > 0 && size <= GUF_STR_SSO_BUF_CAP && str->data.shrt.c_str[size - 1] == '\0';
     } else {
         const size_t cap_with_null = guf_str_cap_internal_(str) + 1;
+        const size_t size = guf_str_size_internal_(str); // len + 1
         const bool valid_cap = cap_with_null > GUF_STR_SSO_BUF_CAP && cap_with_null <= PTRDIFF_MAX && (cap_with_null % 2 == 0);
-        return valid_cap && str->data.lng.c_str && str->data.lng.size > 0 && str->data.lng.size <= cap_with_null;
+        return valid_cap && size >= 1 && str->data.lng.c_str && str->data.lng.size > 0 && str->data.lng.size <= cap_with_null && str->data.lng.c_str[size - 1] == '\0';
     }
 }
 
 GUF_STR_KWRDS guf_str *guf_str_try_reserve(guf_str *str, ptrdiff_t new_cap_min, guf_err *err)
 {
     GUF_ASSERT(guf_str_is_valid(str));
-    GUF_ASSERT(!guf_str_is_readonly(str));
+
+    if (guf_str_is_readonly(str)) {
+        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, GUF_ERR_MSG("in guf_str_try_reserve: guf_str is readonly"));
+        return NULL;
+    } 
 
     const size_t old_cap_with_null = guf_str_cap_internal_(str) + 1;
     const size_t len_with_null = guf_str_len_internal_(str) + 1;
 
-    if (new_cap_min <= (ptrdiff_t)old_cap_with_null) { // No need to grow.
+    if (new_cap_min < (ptrdiff_t)old_cap_with_null) { // No need to grow. TODO: was <=, should be < ?
         guf_err_set_if_not_null(err, GUF_ERR_NONE);
         return str;
     }
@@ -382,6 +397,7 @@ GUF_STR_KWRDS guf_str *guf_str_try_reserve(guf_str *str, ptrdiff_t new_cap_min,
         }
         memcpy(c_str_new, str->data.shrt.c_str, len_with_null);
         str->data.lng.c_str = c_str_new;
+        str->data.lng.size = len_with_null;
         guf_str_set_lng_cap_(str, new_cap_min_with_null);
     } else { // b) Was long string -> need re-allocation
         char *c_str_new = str->allocator->realloc(str->data.lng.c_str, old_cap_with_null, new_cap_min_with_null, str->allocator->ctx);
@@ -398,9 +414,67 @@ GUF_STR_KWRDS guf_str *guf_str_try_reserve(guf_str *str, ptrdiff_t new_cap_min,
     return str;
 }
 
+GUF_STR_KWRDS guf_str *guf_str_reserve(guf_str *str, ptrdiff_t new_cap_min)
+{
+    return guf_str_try_reserve(str, new_cap_min, NULL);
+}
+
+
+GUF_STR_KWRDS guf_str *guf_str_try_shrink_to_fit(guf_str *str, guf_err *err)
+{
+    GUF_ASSERT(guf_str_is_valid(str));
+
+    if (guf_str_is_readonly(str)) {
+        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, GUF_ERR_MSG("in guf_str_try_shrink_to_fit: guf_str is readonly"));
+        return NULL;
+    }
+
+    const size_t old_cap_with_null = guf_str_cap_internal_(str) + 1;
+    const size_t len_with_null = guf_str_len_internal_(str) + 1;
+    GUF_ASSERT(len_with_null <= old_cap_with_null);
+
+    if (old_cap_with_null == len_with_null || guf_str_is_short_internal_(str)) {
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
+        return str;
+    } 
+
+    char *c_str_old = guf_str_cstr(str);
+    GUF_ASSERT(c_str_old);
+
+    if (len_with_null <= GUF_STR_SSO_BUF_CAP) { // a) Shrunk size fits into short.string.
+        GUF_ASSERT(len_with_null <= UCHAR_MAX)
+        guf_str_set_shrt_size_(str, (unsigned char)len_with_null); 
+        memcpy(str->data.shrt.c_str, c_str_old, len_with_null);
+        str->allocator->free(c_str_old, old_cap_with_null, str->allocator->ctx);
+        GUF_ASSERT(guf_str_is_short(str));
+        GUF_ASSERT(guf_str_is_valid(str));
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
+        return str;
+    }
+    // b) Shrunk size does not fit into short-string.
+    char *c_str_new = str->allocator->realloc(c_str_old, old_cap_with_null, len_with_null, str->allocator->ctx);
+    if (!c_str_new) {
+        guf_err_set_or_panic(err, GUF_ERR_ALLOC_FAIL, GUF_ERR_MSG("in guf_str_try_shrink_to_fit: realloc failed"));
+        return NULL;
+    } else {
+        str->data.lng.c_str = c_str_new;
+        guf_str_set_lng_cap_(str, len_with_null);
+        GUF_ASSERT(!guf_str_is_short(str));
+        GUF_ASSERT(guf_str_is_valid(str));
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
+        return str;
+    }
+}
+
+GUF_STR_KWRDS guf_str *guf_str_shrink_to_fit(guf_str *str)
+{
+    return guf_str_try_shrink_to_fit(str, NULL);
+}
+
+
 static char *guf_str_get_cstr_internal_(guf_str *str)
 {
-    if (guf_str_is_short(str)) {
+    if (guf_str_is_short_internal_(str)) {
         return str->data.shrt.c_str;
     } else {
         return str->data.lng.c_str;
@@ -470,14 +544,15 @@ GUF_STR_KWRDS bool guf_str_is_uninit(const guf_str *str)
 
 GUF_STR_KWRDS guf_str *guf_str_init_empty(guf_str *str, guf_allocator *allocator)
 {
-    GUF_ASSERT(str && allocator);
+    GUF_ASSERT_RELEASE(str && allocator);
+    GUF_ASSERT_RELEASE(allocator->alloc && allocator->realloc && allocator->free);
     str->allocator = allocator;
     guf_str_set_shrt_size_(str, 1);
     str->data.shrt.c_str[0] = '\0';
+    GUF_ASSERT(guf_str_is_valid(str));
     return str;
 }
 
-
 GUF_STR_KWRDS guf_str *guf_str_try_init(guf_str *str, guf_str_view str_view, guf_allocator *alloc, guf_err *err)
 {
     if (!str) {
@@ -498,11 +573,14 @@ GUF_STR_KWRDS guf_str *guf_str_try_init(guf_str *str, guf_str_view str_view, guf
     if (str_view.len == 0) {
         GUF_ASSERT(!guf_str_is_readonly(str));
         GUF_ASSERT(guf_str_is_valid(str));
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
         return str;
     }
     GUF_ASSERT(str_view.str && str_view.len > 0);
 
     guf_str_try_reserve(str, str_view.len, err);
+    GUF_ASSERT(guf_str_is_valid(str));
+
     if (err && *err != GUF_ERR_NONE) {
         guf_panic(*err, GUF_ERR_MSG("in guf_str_try_init: Initial allocation failed"));
         return NULL;
@@ -512,9 +590,10 @@ GUF_STR_KWRDS guf_str *guf_str_try_init(guf_str *str, guf_str_view str_view, guf
     GUF_ASSERT(!guf_str_is_readonly(str));
 
     char *c_str_dst = guf_str_get_cstr_internal_(str);
-    GUF_ASSERT_RELEASE(c_str_dst);
+    GUF_ASSERT(c_str_dst);
     memcpy(c_str_dst, str_view.str, str_view.len);
     c_str_dst[str_view.len] = '\0';
+    guf_str_set_len_internal_(str, str_view.len);
 
     GUF_ASSERT(!guf_str_is_readonly(str));
     GUF_ASSERT(guf_str_is_valid(str));
@@ -536,13 +615,65 @@ GUF_STR_KWRDS guf_str guf_str_try_new(guf_str_view str_view, guf_allocator *allo
         return guf_str_new_uninitialised();
     } else {
         GUF_ASSERT(!guf_str_is_uninit(&str));
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
         return str;
     }
 }
 
+GUF_STR_KWRDS guf_str guf_str_new(guf_str_view str_view, guf_allocator *alloc) 
+{
+    return guf_str_try_new(str_view, alloc, NULL);
+}
+
+GUF_STR_KWRDS guf_str *guf_str_try_init_from_cstr(guf_str *str, const char* c_str, guf_allocator *alloc, guf_err *err)
+{
+    GUF_ASSERT(str);
+    if (!str) {
+        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, GUF_ERR_MSG("in guf_str_try_init_from_cstr: str is NULL"));
+        return NULL;
+    } else if (!c_str) {
+        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, GUF_ERR_MSG("in guf_str_try_init_from_cstr: c_str is NULL"));
+        return NULL;
+    } else if (!alloc || !alloc->alloc || !alloc->realloc || !alloc->free) {
+        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, GUF_ERR_MSG("in guf_str_try_init_from_cstr: alloc (or allocs function pointers) is/are NULL"));
+        return NULL;
+    }
+
+    const size_t len = strlen(c_str);
+    if (len >= PTRDIFF_MAX) {
+        guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, GUF_ERR_MSG("in guf_str_try_init_from_cstr: stlen(c_str) >= PTRDIFF_MAX"));
+        return NULL;
+    }
+
+    guf_str_try_init(str, (guf_str_view){.str = c_str, .len = (ptrdiff_t)len}, alloc, err);
+    if (err && *err != GUF_ERR_NONE) {
+        guf_err_set_or_panic(err, *err, GUF_ERR_MSG("in guf_str_try_init_from_cstr: guf_str_try_init failed"));
+        return NULL;
+    } else {
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
+        return str;
+    }
+}
+
+GUF_STR_KWRDS guf_str *guf_str_init_from_cstr(guf_str *str, const char* c_str, guf_allocator *alloc)
+{
+    return guf_str_try_init_from_cstr(str, c_str, alloc, NULL);
+}
+
+GUF_STR_KWRDS guf_str_view guf_str_to_view(const guf_str *str)
+{
+    GUF_ASSERT(guf_str_is_valid(str));
+    guf_str_view sv = {
+        .str = guf_str_const_cstr(str),
+        .len = guf_str_len(str)
+    };
+    GUF_ASSERT(guf_str_view_is_valid(sv));
+    return sv; 
+}
+
 GUF_STR_KWRDS char *guf_str_try_at(guf_str *str, ptrdiff_t idx, guf_err *err)
 {
-    GUF_ASSERT_RELEASE(guf_str_is_valid(str));
+    GUF_ASSERT(guf_str_is_valid(str));
 
     const ptrdiff_t len = guf_str_len(str);
 
@@ -555,6 +686,7 @@ GUF_STR_KWRDS char *guf_str_try_at(guf_str *str, ptrdiff_t idx, guf_err *err)
     } else {
         char *c_str = guf_str_try_get_cstr(str, err);
         if (err && *err != GUF_ERR_NONE) {
+            guf_err_set_or_panic(err, *err, GUF_ERR_MSG("in guf_str_try_at: guf_str_try_get_cstr failed (guf_str is readonly)"));
             return NULL;
         }
         GUF_ASSERT(c_str);
@@ -576,6 +708,7 @@ GUF_STR_KWRDS char *guf_str_try_back(guf_str *str, guf_err *err)
         guf_err_set_or_panic(err, GUF_ERR_IDX_RANGE, GUF_ERR_MSG("in guf_str_try_back: len == 0"));
         return NULL;
     } else {
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
         return guf_str_try_at(str, len - 1, err);
     }
 }
@@ -593,6 +726,7 @@ GUF_STR_KWRDS char *guf_str_try_front(guf_str *str, guf_err *err)
         guf_err_set_or_panic(err, GUF_ERR_IDX_RANGE, GUF_ERR_MSG("in guf_str_try_front: len == 0"));
         return NULL;
     } else {
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
         return guf_str_try_at(str, 0, err);
     }
 }
@@ -604,8 +738,8 @@ GUF_STR_KWRDS char *guf_str_front(guf_str *str)
 
 GUF_STR_KWRDS char guf_str_try_at_cpy(const guf_str *str, ptrdiff_t idx, guf_err *err)
 {
+    GUF_ASSERT(guf_str_is_valid(str));
     const ptrdiff_t len = guf_str_len(str);
-
     if (idx < 0) {
         guf_err_set_or_panic(err, GUF_ERR_IDX_RANGE, GUF_ERR_MSG("in guf_str_try_at_cpy: idx < 0"));
         return '\0';
@@ -633,6 +767,7 @@ GUF_STR_KWRDS char guf_str_try_back_cpy(const guf_str *str, guf_err *err)
         guf_err_set_or_panic(err, GUF_ERR_IDX_RANGE, GUF_ERR_MSG("in guf_str_try_back_cpy: len == 0"));
         return '\0';
     } else {
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
         return guf_str_try_at_cpy(str, len - 1, err);
     }
 }
@@ -650,6 +785,7 @@ GUF_STR_KWRDS char guf_str_try_front_cpy(const guf_str *str, guf_err *err)
         guf_err_set_or_panic(err, GUF_ERR_IDX_RANGE, GUF_ERR_MSG("in guf_str_try_front_cpy: len == 0"));
         return '\0';
     } else {
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
         return guf_str_try_at_cpy(str, 0, err);
     }
 }
@@ -763,17 +899,55 @@ GUF_STR_KWRDS int guf_str_cmp(const guf_str *a, const guf_str *b)
     return memcmp(a_cstr, b_cstr, shorter_len);
 }
 
+GUF_STR_KWRDS guf_str *guf_str_try_set(guf_str *str, guf_str_view sv, guf_err *err)
+{
+    GUF_ASSERT(guf_str_is_valid(str));
+    if (guf_str_is_readonly(str)) {
+        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, GUF_ERR_MSG("in guf_str_try_set: guf_str is readonly"));
+        return NULL;
+    } else if (!guf_str_view_is_valid(sv)) {
+        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, GUF_ERR_MSG("in guf_str_try_set: str_view is invalid"));
+        return NULL;
+    }
+
+    guf_str_try_reserve(str, sv.len, err);
+    if (err && *err != GUF_ERR_NONE) {
+        guf_err_set_or_panic(err, *err, GUF_ERR_MSG("in guf_str_try_set: guf_str_try_reserve failed"));
+        return NULL;
+    } 
+
+    char *c_str_dst = guf_str_cstr(str);
+    GUF_ASSERT(c_str_dst);
+    if (sv.len > 0) {
+        GUF_ASSERT(sv.str);
+        memcpy(c_str_dst, sv.str, sv.len);
+    }
+    c_str_dst[sv.len] = '\0';
+    guf_str_set_len_internal_(str, sv.len);
+
+    GUF_ASSERT(guf_str_is_valid(str));
+    guf_err_set_if_not_null(err, GUF_ERR_NONE);
+    return str;
+}
+
+GUF_STR_KWRDS guf_str *guf_str_set(guf_str *str, guf_str_view sv)
+{
+    return guf_str_try_set(str, sv, NULL);
+}
+
+
+
 GUF_STR_KWRDS guf_str *guf_str_try_append_char(guf_str *str, char c, ptrdiff_t times, guf_err *err)
 {
     GUF_ASSERT(guf_str_is_valid(str));
 
-   if (guf_str_is_readonly(str)) {
-        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_append_char: str is readonly");
+    if (guf_str_is_readonly(str)) {
+        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, GUF_ERR_MSG("in guf_str_try_append_char: str is readonly"));
         return NULL;
     }
 
     if (times < 0) {
-        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, "in guf_str_try_append_char: repeats < 0");
+        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, GUF_ERR_MSG("in guf_str_try_append_char: repeats < 0"));
         return NULL;
     } else if (times == 0) {
         guf_err_set_if_not_null(err, GUF_ERR_NONE);
@@ -787,12 +961,12 @@ GUF_STR_KWRDS guf_str *guf_str_try_append_char(guf_str *str, char c, ptrdiff_t t
 
     const size_t new_len = old_len + (size_t)times;
     if (new_len <= old_len || new_len >= (size_t)PTRDIFF_MAX) { // Handle overflow.
-        guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, "in guf_str_try_append_char: new length would overflow ptrdiff_t");
+        guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, GUF_ERR_MSG("in guf_str_try_append_char: new length would overflow ptrdiff_t"));
         return NULL;
     } else if (new_len > old_cap) { // Need to grow capacity.
         guf_str_try_reserve(str, new_len, err);
         if (err && *err != GUF_ERR_NONE) {
-            guf_err_set_or_panic(err, *err, "in guf_str_try_append_char: failed to reserve capacity");
+            guf_err_set_or_panic(err, *err, GUF_ERR_MSG("in guf_str_try_append_char: failed to reserve capacity"));
             return NULL;
         }
     }
@@ -833,10 +1007,10 @@ GUF_STR_KWRDS guf_str *guf_str_try_append(guf_str *str, guf_str_view sv, guf_err
     GUF_ASSERT(guf_str_is_valid(str));
 
     if (!guf_str_view_is_valid(sv)) {
-        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, "in guf_str_try_append_view: str_view is invalid");
+        guf_err_set_or_panic(err, GUF_ERR_INVALID_ARG, GUF_ERR_MSG("in guf_str_try_append_view: str_view is invalid"));
         return NULL;
     } else if (guf_str_is_readonly(str)) {
-        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in in guf_str_try_append_view: str is readonly");
+        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, GUF_ERR_MSG("in in guf_str_try_append_view: str is readonly"));
         return NULL;
     }
 
@@ -850,12 +1024,12 @@ GUF_STR_KWRDS guf_str *guf_str_try_append(guf_str *str, guf_str_view sv, guf_err
     const size_t old_len = guf_str_len_internal_(str);
     const size_t new_len = old_len + (size_t)sv.len;
     if (new_len <= old_len || new_len >= (size_t)PTRDIFF_MAX) { // Handle overflow.
-        guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, "in guf_str_try_append_view: new length would overflow ptrdiff_t");
+        guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, GUF_ERR_MSG("in guf_str_try_append_view: new length would overflow ptrdiff_t"));
         return NULL;
     }  else if (new_len > old_cap) { // Growth necessary.
         guf_str_try_reserve(str, new_len, err);
         if (err && *err != GUF_ERR_NONE) {
-            guf_err_set_or_panic(err, *err, "in guf_str_try_append_view: failed to reserve capacity");
+            guf_err_set_or_panic(err, *err, GUF_ERR_MSG("in guf_str_try_append_view: failed to reserve capacity"));
             return NULL;
         }
     }
@@ -882,55 +1056,6 @@ GUF_STR_KWRDS guf_str *guf_str_append(guf_str *str, guf_str_view sv)
     return guf_str_try_append(str, sv, NULL);
 }
 
-GUF_STR_KWRDS guf_str *guf_str_try_append_cstr(guf_str *str, const char *c_str, guf_err *err)
-{
-    GUF_ASSERT(guf_str_is_valid(str));
-
-    if (!c_str) {
-        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_append_cstr: c_str is NULL");
-        return NULL;
-    } else if (guf_str_is_readonly(str)) {
-        guf_err_set_or_panic(err, GUF_ERR_NULL_PTR, "in guf_str_try_append_cstr: str is readonly");
-        return NULL;
-    }
-
-    char *dst_cstr = guf_str_get_cstr_internal_(str);
-    size_t i = 0;
-    do {
-        size_t cap = guf_str_cap_internal_(str); 
-        size_t len = guf_str_len_internal_(str);
-        GUF_ASSERT(len <= cap);
-
-        if (len == cap) { // Grow if necessary. 
-            if (cap == PTRDIFF_MAX) {
-                guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, "in guf_str_try_append_cstr: cannot grow (capacity is PTRDIFF_MAX)");
-                return NULL;
-            }
-            guf_str_try_reserve(str, cap + 1, err);
-            if (err && *err != GUF_ERR_NONE) {
-                guf_err_set_or_panic(err, GUF_ERR_INT_OVERFLOW, "in guf_str_try_append_cstr: failed to reserve");
-                return NULL;
-            }
-            cap = guf_str_cap_internal_(str); 
-            len = guf_str_len_internal_(str);
-        }
-
-        dst_cstr[len] = c_str[i];
-        guf_str_set_len_internal_(str, len + 1);
-    } while (c_str[i++] != '\0');
-
-    GUF_ASSERT(guf_str_is_valid(str));
-    GUF_ASSERT(dst_cstr[guf_str_len_internal_(str)] == '\0');
-
-    guf_err_set_if_not_null(err, GUF_ERR_NONE);
-    return str;
-}
-
-GUF_STR_KWRDS guf_str *guf_str_append_cstr(guf_str *str, const char *c_str)
-{
-    return guf_str_try_append_cstr(str, c_str, NULL);
-}
-
 GUF_STR_KWRDS guf_str *guf_str_try_substr(guf_str *str, ptrdiff_t pos, ptrdiff_t count, guf_err *err)
 {
     GUF_ASSERT(guf_str_is_valid(str));
@@ -975,6 +1100,33 @@ GUF_STR_KWRDS guf_str *guf_str_substr(guf_str *str, ptrdiff_t pos, ptrdiff_t cou
     return guf_str_try_substr(str, pos, count, NULL);
 }
 
+GUF_STR_KWRDS char guf_str_try_pop_back(guf_str *str, guf_err *err)
+{
+    GUF_ASSERT(guf_str_is_valid(str));
+
+    const ptrdiff_t len = guf_str_len(str);
+    if (len <= 0) {
+        guf_err_set_or_panic(err, GUF_ERR_IDX_RANGE, GUF_ERR_MSG("in guf_str_try_pop_back: len <= 0"));
+        return '\0';
+    }
+    GUF_ASSERT(len - 1 >= 0);
+    const char last = guf_str_at_cpy(str, len - 1);
+    guf_str_try_substr(str, 0, len - 1, err);
+    if (err && *err != GUF_ERR_NONE) {
+        guf_err_set_or_panic(err, *err, GUF_ERR_MSG("in guf_str_try_pop_back: guf_str_try_substr failed"));
+        return '\0';
+    } else {
+        GUF_ASSERT(guf_str_is_valid(str));
+        GUF_ASSERT(guf_str_len(str) == len - 1);
+        guf_err_set_if_not_null(err, GUF_ERR_NONE);
+        return last;
+    }
+}
+
+GUF_STR_KWRDS char guf_str_pop_back(guf_str *str)
+{
+    return guf_str_try_pop_back(str, NULL);
+}
 
 
 // guf_str_view:
diff --git a/src/test/test.cpp b/src/test/test.cpp
index 2646288..5a4b6a5 100644
--- a/src/test/test.cpp
+++ b/src/test/test.cpp
@@ -11,6 +11,7 @@ extern "C" {
 #include "test_dbuf.hpp"
 #include "test_dict.hpp"
 #include "test_utf8.hpp"
+#include "test_str.hpp"
 
 std::unordered_set<std::unique_ptr<Test>> g_tests {};
 
@@ -31,6 +32,10 @@ void init_tests()
     test = std::make_unique<UTF8Test>("UTF8Test");
     GUF_ASSERT_RELEASE(test.get());
     g_tests.insert(std::move(test));
+
+    test = std::make_unique<StrTest>("StrTest");
+    GUF_ASSERT_RELEASE(test.get())
+    g_tests.insert(std::move(test));
 }
 
 int main()
diff --git a/src/test/test_str.hpp b/src/test/test_str.hpp
new file mode 100644
index 0000000..4e4562a
--- /dev/null
+++ b/src/test/test_str.hpp
@@ -0,0 +1,212 @@
+#include <vector>
+#include <string>
+
+#include "test.hpp"
+
+extern "C" {
+    #include "guf_alloc_libc.h"
+    #include "guf_str.h"
+}
+
+struct StrTest : public Test 
+{
+public: 
+    StrTest(const std::string& name) : Test(name) {};
+
+private:
+    void test_init_free(std::string str)
+    {
+        guf_str s0; 
+        guf_str_init(&s0, GUF_CSTR_TO_VIEW_CPP(str.c_str()), &guf_allocator_libc);
+        guf_str s1 = guf_str_new(GUF_CSTR_TO_VIEW_CPP(str.c_str()), &guf_allocator_libc);
+        guf_str s2; 
+        guf_str_init_from_cstr(&s2, str.c_str(), &guf_allocator_libc);    
+
+        TEST_CHECK(guf_str_equal(&s0, &s1));
+        TEST_CHECK(guf_str_equal(&s0, &s2));
+        TEST_CHECK(guf_str_equal(&s1, &s2));
+        
+        TEST_CHECK((ptrdiff_t)str.size() == guf_str_len(&s0));
+        TEST_CHECK(str == guf_str_const_cstr(&s0));
+        TEST_CHECK(str == guf_str_cstr(&s0));
+
+        TEST_CHECK((ptrdiff_t)str.size() == guf_str_len(&s1));
+        TEST_CHECK(str == guf_str_const_cstr(&s1));
+        TEST_CHECK(str == guf_str_cstr(&s1));
+
+        TEST_CHECK((ptrdiff_t)str.size() == guf_str_len(&s2));
+        TEST_CHECK(str == guf_str_const_cstr(&s2));
+        TEST_CHECK(str == guf_str_cstr(&s2));
+
+        guf_str_free(&s0, NULL);
+        guf_str_free(&s1, NULL);
+        guf_str_free(&s2, NULL);
+        TEST_CHECK(guf_str_is_uninit(&s0));
+        TEST_CHECK(guf_str_is_uninit(&s1));
+        TEST_CHECK(guf_str_is_uninit(&s2));
+    }
+
+    void test_init_empty()
+    {
+        std::string str = "";
+        guf_str s = GUF_STR_UNINITIALISED_CPP;
+        guf_str_init_empty(&s, &guf_allocator_libc);
+        TEST_CHECK(guf_str_len(&s) == 0);
+        TEST_CHECK(str == guf_str_const_cstr(&s));
+
+        guf_str_append_char(&s, 'a', 1024); 
+        str.append(1024, 'a');
+        TEST_CHECK(guf_str_len(&s) == (ptrdiff_t)str.size());
+        TEST_CHECK(guf_str_const_cstr(&s) == str);
+
+        guf_str_append_char(&s, 'b', 24); 
+        str.append(24, 'b');
+        TEST_CHECK(guf_str_len(&s) == (ptrdiff_t)str.size());
+        TEST_CHECK(guf_str_const_cstr(&s) == str);
+
+        guf_str_append_char(&s, 'c', 255); 
+        str.append(255, 'c');
+        TEST_CHECK(guf_str_len(&s) == (ptrdiff_t)str.size());
+        TEST_CHECK(guf_str_const_cstr(&s) == str);
+
+        *guf_str_at(&s, 0) = '<';
+        str.at(0) = '<';
+        TEST_CHECK(guf_str_len(&s) == (ptrdiff_t)str.size());
+        TEST_CHECK(guf_str_const_cstr(&s) == str);
+
+        *guf_str_at(&s, guf_str_len(&s) - 1) = '>';
+        str.at(str.size() - 1) = '>';
+        TEST_CHECK(guf_str_len(&s) == (ptrdiff_t)str.size());
+        TEST_CHECK(guf_str_const_cstr(&s) == str);
+
+        guf_err err = GUF_ERR_NONE;
+        TEST_CHECK(NULL == guf_str_try_at(&s, guf_str_len(&s), &err));
+        TEST_CHECK(err != GUF_ERR_NONE && err == GUF_ERR_IDX_RANGE); 
+        err = GUF_ERR_NONE; 
+        TEST_CHECK(NULL == guf_str_try_at(&s, -1, &err));
+        TEST_CHECK(err != GUF_ERR_NONE && err == GUF_ERR_IDX_RANGE); 
+
+        guf_str_free(&s, NULL);
+        TEST_CHECK(guf_str_is_uninit(&s));
+    }
+
+    void test_append_char(std::string str, bool include_null = false)
+    {
+        guf_str s0 = guf_str_new(guf_str_view{.str = str.c_str(), .len = (ptrdiff_t)str.size()}, &guf_allocator_libc);
+
+        TEST_CHECK((ptrdiff_t)str.size() == guf_str_len(&s0));
+        TEST_CHECK((str == std::string_view{guf_str_const_cstr(&s0), (size_t)guf_str_len(&s0)}));
+
+        for (int i = include_null ? 0 : 1; i < 128; ++i) { 
+            char ch = (char)i;
+            guf_str_append_one_char(&s0, ch);
+            str.append(1, ch);
+            TEST_CHECK(guf_str_len(&s0) == (ptrdiff_t)str.size());
+            TEST_CHECK((str == std::string_view{guf_str_const_cstr(&s0), (size_t)guf_str_len(&s0)}));
+        }
+
+        for (int i = include_null ? 0 : 1; i < 128; ++i) {
+            char ch = (char)i;
+            guf_str_append_char(&s0, ch, i);
+            str.append(i, ch);
+            TEST_CHECK(guf_str_len(&s0) == (ptrdiff_t)str.size());
+            TEST_CHECK((str == std::string_view{guf_str_const_cstr(&s0), (size_t)guf_str_len(&s0)}));
+            guf_str_append_char(&s0, ch, i * 16);
+            str.append(i * 16, ch);
+            TEST_CHECK(guf_str_len(&s0) == (ptrdiff_t)str.size());
+            TEST_CHECK((str == std::string_view{guf_str_const_cstr(&s0), (size_t)guf_str_len(&s0)}));
+        }
+
+        guf_str_free(&s0, NULL);
+        TEST_CHECK(guf_str_is_uninit(&s0));
+    }
+
+    void append_str(const std::string& a, const std::string& b)
+    {
+            std::string str0 = a;
+            guf_str s0 = guf_str_new(guf_str_view{.str = str0.c_str(), .len = (ptrdiff_t)str0.size()}, &guf_allocator_libc);
+            TEST_CHECK(guf_str_len(&s0) == (ptrdiff_t)str0.size());
+            TEST_CHECK((str0 == std::string_view{guf_str_const_cstr(&s0), (size_t)guf_str_len(&s0)}));
+            TEST_CHECK((str0 == std::string_view{guf_str_cstr(&s0), (size_t)guf_str_len(&s0)}));
+
+            for (int i = 0; i <= 64; ++i) {
+                str0.append(b);
+                guf_str_append(&s0, guf_str_view{.str = b.c_str(), .len = (ptrdiff_t)b.size()});
+                TEST_CHECK(guf_str_len(&s0) == (ptrdiff_t)str0.size());
+                TEST_CHECK((str0 == std::string_view{guf_str_const_cstr(&s0), (size_t)guf_str_len(&s0)}));
+                TEST_CHECK((str0 == std::string_view{guf_str_cstr(&s0), (size_t)guf_str_len(&s0)}));
+            }
+
+            guf_str_free(&s0, NULL);
+            TEST_CHECK(guf_str_is_uninit(&s0));
+    }
+ 
+public:
+    bool run()
+    {
+        if (done) {
+            return passed;
+        }
+
+        const std::vector<std::string> words = {
+            "",
+            "\0",
+            "Hello", 
+            "Othell\0o",
+            "f\0\0",
+            "\0",
+            "0",
+            "a", 
+            "ab", 
+            "🌈 waow a rainboge!",
+            "orange cat(1) :3",
+            "xes yag",
+            "Hello, world! This is a pretty darn long string I'd say...", 
+            "I want to eat crayons. I crave crayons because they are tasty, and everybody telling me crayons are not edible must be either lying or dumb. I like trains. 42 is a number. 3.14159265... is not a rational number, and it is called pi. I ate some pie (it was a crayon pie).", 
+            std::string(32, 'a'),
+            std::string(64, 'b'),
+            std::string(1024, 'a'),
+            std::string(2048, 'a'),
+            std::string(4096, 'a'),
+            std::string(5001, 'a'),
+            std::string(7121, 'a'),
+            std::string(2000, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP - 1, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP + 1, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP - 2, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP + 2, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP - 3, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP + 3, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP * 2, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP * 3, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP * 4, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP * 5, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP * 6, 'a'),
+            std::string(GUF_STR_SSO_BUF_CAP * 7, 'a'),
+        };
+
+        test_init_empty();
+
+        for (const auto& word : words) {
+            test_init_free(word);
+            test_append_char(word); 
+            test_append_char(word, true);
+        }
+
+        for (size_t i = 0; i < words.size(); ++i) {
+            const auto& w1 = words.at(i);
+            append_str(w1, w1);
+            append_str(w1, w1);
+            for (size_t j = i + 1; j < words.size(); ++j) {
+                const auto& w2 = words.at(j);
+                append_str(w1, w2);
+                append_str(w2, w1);
+            }
+        }
+
+        done = true;
+        passed = (num_failed_checks == 0);
+        return passed;
+    }
+}; 
\ No newline at end of file
diff --git a/todo.txt b/todo.txt
index 2af0728..79eca7f 100644
--- a/todo.txt
+++ b/todo.txt
@@ -9,7 +9,6 @@
 
 - guf_stack, guf_queue, guf_dqueue, guf_prio_queue (using a heap), guf_ringbuf
 
-
 - track allocs for test (implement alloc tracker):
    - each thread needs its own alloc and alloc_ctx; don't track granular, give each allocator it's unique id maybe?