Feat: Add generators for String type

Update README with string generators no longer missing.

Author: jockbert

DOCUMENTATION.md

@@ -214,14 +214,21 @@ let some_longs = gens::i64::ranged(10..=20);
 let mostly_true = gens::bool::with_ratio(1,20);
 ```
 
-Various generators for `char` type:
+Various generators for types `char` and `String`:
 
 ```rust
 use monkey_test::*;
 let same_as_unicode = gens::char::any();
 let unicode = gens::char::unicode();
 let alpha_lower = gens::char::alpha_lower();
 let alpha_numeric = gens::char::alpha_numeric();
+
+let alpha_upper_string = gens::string::alpha_upper();
+let any_string_starting_with_a_of_length_5 =
+    gens::string::any().of_size(4..=4).map(
+        |str_suffix| format!("A{}", str_suffix),
+        |str_with_prefix_a| str_with_prefix_a.clone()[1..].to_string(),
+    );
 ```
 
 There are also specialized generators:

README.md

@@ -59,7 +59,6 @@ Currently, in versions 0.x.y, the library is in active development.
 It is currently missing some parts, primarily built in generators
 and shrinkers for:
 
-* Strings.
 * Commonly used data structures besides `Vec`.
 * Recursive data structures.
 

src/gens.rs

@@ -16,6 +16,7 @@ mod of_size;
 mod other_shrink;
 mod pick;
 pub mod sized;
+pub mod string;
 pub mod vec;
 mod zip;
 

src/gens/string.rs

@@ -0,0 +1,73 @@
+//! Generators for String type.
+
+use crate::BoxGen;
+use crate::MapWithGen;
+
+/// Build String generator from char generator.
+fn strings_from_chars(chars: BoxGen<char>) -> BoxGen<String> {
+    crate::gens::vec::any(chars)
+        .map(|v| v.into_iter().collect(), |s| s.chars().collect())
+}
+
+/// Strings of any possible Rust `char` value, that is any valid unicode scalar
+/// value.
+///
+/// For implementation details, see [crate::gens::char::unicode].
+pub fn unicode() -> BoxGen<String> {
+    strings_from_chars(crate::gens::char::unicode())
+}
+
+/// Shorthand for [unicode].
+pub fn any() -> BoxGen<String> {
+    unicode()
+}
+
+/// Strings of any arabic numeral 0..9.
+///
+/// For implementation details, see [crate::gens::char::number].
+pub fn number() -> BoxGen<String> {
+    strings_from_chars(crate::gens::char::number())
+}
+
+/// Strings of any alpha upper char.
+///
+/// For implementation details, see [crate::gens::char::alpha_upper].
+pub fn alpha_upper() -> BoxGen<String> {
+    strings_from_chars(crate::gens::char::alpha_upper())
+}
+
+/// Strings of any alpha lower char.
+///
+/// For implementation details, see [crate::gens::char::alpha_lower].
+pub fn alpha_lower() -> BoxGen<String> {
+    strings_from_chars(crate::gens::char::alpha_lower())
+}
+
+/// Strings of any alpha char.
+///
+/// For implementation details, see [crate::gens::char::alpha].
+pub fn alpha() -> BoxGen<String> {
+    strings_from_chars(crate::gens::char::alpha())
+}
+
+/// Strings of any alpha numeric char.
+///
+/// For implementation details, see [crate::gens::char::alpha_numeric].
+pub fn alpha_numeric() -> BoxGen<String> {
+    strings_from_chars(crate::gens::char::alpha_numeric())
+}
+
+/// Strings of any ASCII printable character.
+///
+/// For implementation details, see [crate::gens::char::ascii_printable].
+pub fn ascii_printable() -> BoxGen<String> {
+    strings_from_chars(crate::gens::char::ascii_printable())
+}
+
+/// Strings of any ASCII character, including both printable and non-printable
+/// characters.
+///
+/// For implementation details, see [crate::gens::char::ascii].
+pub fn ascii() -> BoxGen<String> {
+    strings_from_chars(crate::gens::char::ascii())
+}