Values

Templates contain expressions, and expressions evaluate to values. Template values are basically JSON values, with the addition of one more type: bytes. Here’s the full list:

• null
• boolean: true or false
• float
  • Uses f64 internally. See docs for information on min/max values.
• integer (signed integer)
  • Uses i64 internally. See docs for information on min/max values.
• string: "hello!" or 'hello!'
  • Single-quote format is more common because your templates will often be wrapped in " to denote a YAML string
• bytes: b"hello!" or b'hello!'
• array: [1, false, 'hello!']
• object: { 'a': 1, 'b': 2 }
  • Object keys must be strings. If a non-string value is given, it will be stringified

bytes vs string

A string is technically a subset of bytes: any sequence of valid UTF-8 bytes can be a string. Many functions return a bytes value because Slumber doesn’t know if the value is valid UTF-8 or not. You may wonder: what do I do with this? How do I turn it into a string? You don’t have to! There are three scenarios in which bytes can be used:

• You have a bytes but need a string. The bytes are valid UTF-8. Slumber will automatically convert it to a string when necessary.
• You have a bytes but need a string. The bytes are not valid UTF-8. Slumber will attempt to convert it to a string and fail, returning an error during request render.
• You have a bytes and need a bytes (e.g. for a request body, which doesn’t need to be valid UTF-8). Easy!

So the short answer is: if you see a function return bytes, you can generally pretend it says string. The types are distinct to acknowledge the fact that the bytes may not be valid UTF-8, and therefore may trigger errors while rendering a request.