gleam/string_builder

Types

StringBuilder

StringBuilder is a type used for efficiently building strings.

When we append one string to another the strings must be copied to a new location in memory so that they can sit together. This behaviour enables efficient reading of the string but copying can be expensive, especially if we want to join many strings together.

StringBuilder is different in that it can be joined together in constant time using minimal memory, and then can be efficiently converted to a string using the to_string function.

pub external type StringBuilder

Functions

append

pub external fn append(
  to: StringBuilder,
  suffix: String,
) -> StringBuilder

Append a String onto the end of some StringBuilder.

Runs in constant time.

append_builder

pub external fn append_builder(
  to: StringBuilder,
  suffix: StringBuilder,
) -> StringBuilder

Append some StringBuilder onto the end of another.

Runs in constant time.

byte_size

pub external fn byte_size(StringBuilder) -> Int

Returns the size of the StringBuilder in bytes.

concat

pub external fn concat(List(StringBuilder)) -> StringBuilder

Joins a list of builders into a single builder.

Runs in constant time.

from_float

pub external fn from_float(Float) -> StringBuilder

Creates a builder containing the textual representation of a given float.

from_string

pub external fn from_string(String) -> StringBuilder

Convert a string into a builder.

Runs in constant time.

from_strings

pub external fn from_strings(List(String)) -> StringBuilder

Convert a list of strings into a builder.

Runs in constant time.

is_empty

pub external fn is_empty(StringBuilder) -> Bool

Inspect a builder to determine if it is equivalent to an empty string.

Examples

> new("ok") |> is_empty
False

> new("") |> is_empty
True

> from_strings([]) |> is_empty
True

is_equal

pub external fn is_equal(StringBuilder, StringBuilder) -> Bool

Compare two builders to determine if they have the same textual content.

Comparing two iodata using the == operator may return False even if they have the same content as they may have been build in different ways, so using this function is often preferred.

Examples

> from_strings(["a", "b"]) == new("ab")
False

> is_equal(from_strings(["a", "b"]), new("ab"))
True

lowercase

pub external fn lowercase(StringBuilder) -> StringBuilder

Converts a builder to a new builder where the contents have been lowercased.

prepend

pub external fn prepend(
  to: StringBuilder,
  prefix: String,
) -> StringBuilder

Prepend a String onto the start of some StringBuilder.

Runs in constant time.

prepend_builder

pub external fn prepend_builder(
  to: StringBuilder,
  prefix: StringBuilder,
) -> StringBuilder

Prepend some StringBuilder onto the start of another.

Runs in constant time.

replace

pub fn replace(
  in iodata: StringBuilder,
  each pattern: String,
  with substitute: String,
) -> StringBuilder

Replaces all instances of a pattern with a given string substitute.

reverse

pub external fn reverse(StringBuilder) -> StringBuilder

Converts a builder to a new builder with the contents reversed.

split

pub fn split(
  iodata: StringBuilder,
  on pattern: String,
) -> List(StringBuilder)

Splits a builder on a given pattern into a list of builders.

to_string

pub external fn to_string(StringBuilder) -> String

Turns an StringBuilder into a String

This function is implemented natively by the virtual machine and is highly optimised.

uppercase

pub external fn uppercase(StringBuilder) -> StringBuilder

Converts a builder to a new builder where the contents have been uppercased.