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Type Literals

When designing APIs, it’s common to define the structure of the API in terms of specific literal values. For instance, an operation might return a specific integer status code, or a model member might be one of a few specific string values. It’s also useful to pass specific literal values to decorators. TypeSpec supports string, number, and boolean literal values to cater to these needs.

String literals

String literals are represented using double quotes ".

alias Str = "Hello World!";

Multi-line string literals

Multi-line string literals are denoted using three double quotes """.

alias Str = """
  This is a multi line string
   - opt 1
   - opt 2
  """;
  • The opening """ must be followed by a new line.
  • The closing """ must be preceded by a new line.

Trimming indentation in multi-line strings

Multi-line strings automatically trim leading whitespaces on each line to align with the closing """. This feature is handy for maintaining the indentation of multi-line strings within the code without worrying about undesired indentation.

All the following options will yield the same string value "one\ntwo".

model MultiLineContainer {
  prop1: """
one
two
""")


  // Lines are indented at the same level as closing """"
  prop2: """
  one
  two
  """


  prop3: """
      one
      two
      """


  // lines are less indented as the closing """"
  prop4: """
    one
    two
      """
}

String template literal

Both single and multi-line string literals can be interpolated using ${}.

alias hello = "bonjour";
alias Single = "${hello} world!";


alias Multi = """
  ${hello}
  world!
  """;

Any valid expression can be used in the interpolation, but only other literals will result in the template literal being assignable to a valueof string. Any other value will depend on the decorator/emitter receiving it for handling.

Numeric literal

Numeric literals are declared by using the raw number.

alias Kilo = 1000;
alias PI = 3.14;

Boolean literal

Boolean literals are declared by using the true or false keywords.

alias InTypeSpec = true;
alias Cheater = false;