Type inference
Overview
Type inference occurs in Carbon
when the auto keyword is used. This may occur in
variable declarations or function declarations.
At present, type inference is very simple: given the expression which generates
the value to be used for type inference, the inferred type is the precise type
of that expression. For example, the inferred type for auto in
fn Foo(x: i64) -> auto { return x; } is i64.
Type inference is currently supported for function return types and declared variable types.
Open questions
Inferring a variable type from literals
Using the type on the right side for var y: auto = 1 currently results in a
constant IntLiteral(1) value, whereas most languages would suggest a variable
integer type, such as i64. Carbon might also make it an error. Although type
inference currently only addresses auto for variables and function return
types, this is something that will be considered as part of type inference in
general, because it also affects generics, templates, lambdas, and return types.
Alternatives considered
References
- Proposal #851: auto keyword for vars