Crate const_str

Compile-time string operations. See the macro list for what you need.

MSRV: Rust 1.77.0

Troubleshoot

You don’t have to care about this section unless you come across some compile errors about const evaluation.

error[E0435]: attempt to use a non-constant value in a constant

There are mainly two kinds of macros in this crate, which have different requirements for the arguments.

• const-context only
• const-fn compatible

const-context only

These macros can only be used in const contexts. The expanded code is equivalent to compute new constant items. It implies that the arguments of these macros must be constant values, similar to consteval in C++ world.

The following examples will not work:

const fn foo(a: &str, b: &str) -> &str {
   const_str::concat!(a, b)
}

const C: &str = {
    let a = "Hello";
    let b = "World";
    const_str::concat!(a, b);
};

Instead, this way will work:

const A: &str = "Hello";
const B: &str = "World";
const C: &str = const_str::concat!(A, " ", B);
assert_eq!(C, "Hello World");

const-fn compatible

These macros can be used in const contexts and const functions. The expanded code is equivalent to calling const functions. It implies that the arguments of these macros can be any expressions, similar to constexpr in C++ world.

const fn calc(y: &str, m: &str, d: &str) -> u64 {
    let y = const_str::parse!(y, u64);
    let m = const_str::parse!(m, u64);
    let d = const_str::parse!(d, u64);
    (y * 10000 + m * 100 + d)
}
const TIME: u64 = calc("2025", "01", "26");
assert_eq!(TIME, 20250126);

You can also use these macros in normal functions, but they may be much slower than the runtime equivalents. It’s recommended to use them only if you need compile-time evaluation.

Macros

chain

Chains multiple macro calls together.

compare

Compares two strings lexicographically.

concat

Concatenates values into a string slice.

concat_bytes

Concatenates values into a byte slice.

contains

Returns true if the given pattern matches a sub-slice of this string slice.

convert_ascii_case

Converts a string slice to a specified case. Non-ascii characters are not affected.

convert_caseproc or case

Converts a string literal to a specified case.

cstr

Converts a string slice to &CStr.

encode

Encode a string slice with a specified encoding.

encode_z

Encode a string slice with a specified encoding and append a nul character.

ends_with

Returns true if the given pattern matches a suffix of this string slice.

eq_ignore_ascii_case

Checks that two (string) slices are an ASCII case-insensitive match.

equal

Checks that two strings are equal.

formatproc

Creates a string slice using interpolation of const expressions.

from_utf8

Converts a byte string to a string slice

hex

Converts hexadecimal string slices to a byte array.

ip_addr

Converts a string slice to an IP address.

is_ascii

Checks if all characters in this (string) slice are within the ASCII range.

join

Concatenates string slices into a string slice, separated by a given separator.

parse

Parse a value from a string slice.

raw_cstr

Converts a string slice to *const c_char.

regex_assert_matchregex

Asserts that the string literal matches the pattern.

repeat

Creates a new string slice by repeating a string slice n times.

replace

Replaces all matches of a pattern with another string slice.

sorted

Sorts string slices and returns a new array.

split

Returns an array of substrings of a string slice, separated by characters matched by a pattern.

split_inclusive

Returns an array of substrings of a string slice, separated by characters matched by a pattern.

split_lines

Returns an array of the lines in a string.

squish

Splits the string by ASCII whitespaces, and then joins the parts with a single space.

starts_with

Returns true if the given pattern matches a prefix of this string slice.

strip_prefix

Returns a string slice with the prefix removed.

strip_suffix

Returns a string slice with the suffix removed.

to_byte_array

Converts a string slice or a byte string to a byte array.

to_char_array

Converts a string slice into an array of its characters.

to_str

Converts a value to a string slice.

unwrap

Unwraps a container, returns the content.

verified_header_namehttp

Returns a compile-time verified header name string literal.

verified_regexregex

Returns a compile-time verified regex string literal.