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

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

Appends a String onto the end of some StringBuilder.

Runs in constant time.

append_builder

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

Appends some StringBuilder onto the end of another.

Runs in constant time.

byte_size

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pub external fn byte_size(StringBuilder) -> Int

Returns the size of the StringBuilder in bytes.

concat

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

Joins a list of builders into a single builder.

Runs in constant time.

from_float

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pub external fn from_float(Float) -> StringBuilder

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

from_string

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pub external fn from_string(String) -> StringBuilder

Converts a string into a builder.

Runs in constant time.

from_strings

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

Converts a list of strings into a builder.

Runs in constant time.

is_empty

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pub external fn is_empty(StringBuilder) -> Bool

Inspects 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

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

Compares 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

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pub external fn lowercase(StringBuilder) -> StringBuilder

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

prepend

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

Prepends a String onto the start of some StringBuilder.

Runs in constant time.

prepend_builder

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

Prepends some StringBuilder onto the start of another.

Runs in constant time.

replace

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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

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pub external fn reverse(StringBuilder) -> StringBuilder

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

split

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

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

to_string

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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

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pub external fn uppercase(StringBuilder) -> StringBuilder

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