--- title: std canonical_url: https://mew-lang.org/stdlib/std/ sidecar_url: https://mew-lang.org/stdlib/std.md content_hash: sha256:afe18e9b3f6c739bed988356faf6cb709e1b9b9830ee9a978ccd9ba4db209220 tokens: 1737 uid: stdlib.std reading_time_minutes: 7 --- Standard Library # std ## Unions Union Description Option A value that may be missing. Result The result of an operation that can fail. ## Interfaces Interface Description Display Formats a value as text when it is interpolated. Enumerable Exposes an enumerator over a collection of `T`. Enumerator Iterates over an `Enumerable`. Into Converts a value into a `T`. ## Types Type Description ArrayEnumerable Wraps an array as an `Enumerable`. ArrayEnumerator Iterates over an array. FilterEnumerable What `filter` returns. FilterEnumerator Iterates over a `FilterEnumerable`. MapEnumerable What `map` returns. MapEnumerator Iterates over a `MapEnumerable`. ## Functions Function Description `args() -> string[]` Returns the arguments the program was run with, without the program name. `eprint(value: string)` Writes the text to standard error. `eprintln(value: string)` Writes the text to standard error, then a line break. `exit(code: i32 = 0)` Ends the program with the specified code. [noreturn](https://mew-lang.org/language/attributes.md#noreturn) `panic(reason: string)` Writes the reason to standard error and ends the program with code 1. With `MEW_BACKTRACE=1` set, it also writes the calls that led to it. [noreturn](https://mew-lang.org/language/attributes.md#noreturn) `print(value: string)` Writes the text to standard output. `println(value: string)` Writes the text to standard output, then a line break. ## Extensions Type Description string What `std` adds to `string` ## `Option` Case Description `none` No value. `some(T)` A value. Member Description `is_some() -> bool` Whether there is a value. `is_none() -> bool` Whether there is no value. `unwrap() -> T` Returns the value, or panics if there is none. `unwrap_or(fallback: T) -> T` Returns the value, or `fallback` if there is none. `or(other: Option) -> Option` Returns this option if it has a value, otherwise `other`. `map(f: fn(T) -> U) -> Option` Applies `f` to the value, if there is one. `and_then(f: fn(T) -> Option) -> Option` Calls `f` with the value, if there is one, and returns its result. `filter(f: fn(T) -> bool) -> Option` Returns this option if `f` returns true for its value, otherwise `none`. `ok_or(error: E) -> Result` Converts the option into a `Result`, with `error` when there is no value. ## `Result` Case Description `ok(T)` The operation succeeded, with its value. `err(E)` The operation failed, with its error. Member Description `is_ok() -> bool` Whether the result is `ok`. `is_err() -> bool` Whether the result is `err`. `unwrap() -> T` Returns the value, or panics if the result is `err`. `unwrap_or(fallback: T) -> T` Returns the value, or `fallback` if the result is `err`. `map(f: fn(T) -> U) -> Result` Applies `f` to the value, if the result is `ok`. `map_err(f: fn(E) -> F) -> Result` Applies `f` to the error, if the result is `err`. `and_then(f: fn(T) -> Result) -> Result` Calls `f` with the value, if the result is `ok`, and returns its result. `ok() -> Option` Returns the value as an `Option`. `err() -> Option` Returns the error as an `Option`. ## `Display` Member Description `display() -> string` Required. Returns the value as text. ## `Enumerable` Member Description `iter() -> Enumerator` Required. Returns an enumerator positioned before the first element. `map(apply: fn(T) -> U) -> Enumerable` Returns a sequence that applies `apply` to each element. `filter(keep: fn(T) -> bool) -> Enumerable` Returns a sequence of the elements that `keep` returns true for. `fold(seed: A, combine: fn(A, T) -> A) -> A` Combines the elements with `combine`, starting from `seed`. `find(keep: fn(T) -> bool) -> Option` Returns the first element that `keep` returns true for. `any(keep: fn(T) -> bool) -> bool` Whether `keep` returns true for any element. `count() -> i32` Returns the number of elements. `to_array() -> T[]` Copies the elements into an array. ## `Enumerator` Member Description `next() -> bool` Required. Moves to the next element. Returns false when there are none left. `current() -> T` Required. Returns the current element. ## `Into` Member Description `into() -> T` Required. Returns the value converted into a `T`. ## `ArrayEnumerable` Implements `Enumerable`. Field Description `items: T[]` The wrapped array. ## `ArrayEnumerator` Implements `Enumerator`. Field Description `items: T[]` The array to iterate over. `mut at: i32` The index of the current element, or `-1` before the first. ## `FilterEnumerable` Implements `Enumerable`. Field Description `source: Enumerable` The sequence to filter. `keep: fn(T) -> bool` Returns true for the elements to keep. ## `FilterEnumerator` Implements `Enumerator`. Field Description `source: Enumerator` The enumerator to filter. `keep: fn(T) -> bool` Returns true for the elements to keep. ## `MapEnumerable` Implements `Enumerable`. Field Description `source: Enumerable` The sequence to map. `apply: fn(T) -> U` The function to apply to each element. ## `MapEnumerator` Implements `Enumerator`. Field Description `source: Enumerator` The enumerator to map. `apply: fn(T) -> U` The function to apply to each element. ## `string` Member Description `is_empty() -> bool` Whether the string is empty. `parse_i32() -> Result` Parses the string into an `i32`. `length() -> i32` Gets the length of the string, in Unicode code points. `starts_with(prefix: string) -> bool` Whether the string begins with `prefix`. `skip(count: i32) -> string` Returns what is left after the first `count` characters. `split(separator: char) -> string[]` Splits the string at each `separator`, keeping empty parts. `lines() -> string[]` Splits the string into lines. `trim_end() -> string` Removes trailing spaces, tabs and line breaks. `pad_left(width: i32) -> string` Pads the string with spaces on the left to `width` characters. `pad_right(width: i32) -> string` Pads the string with spaces on the right to `width` characters. `string::join(separator: string, parts: ...string) -> string` Joins the parts with `separator` between them. `string::join(separator: string, items: Enumerable) -> string` Joins the items with `separator` between them. 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