Type operators

Table of contents

• Overview
• Details
  • Precedence
• Alternatives considered
• References

Overview

Carbon provides the following operators to transform types:

• const as a prefix unary operator produces a const-qualified type.
• * as a postfix unary operator produces a pointer type to some other type.

The pointer type operator is also covered as one of the pointer operators.

Details

The semantic details of both const-qualified types and pointer types are provided as part of the values design:

• const-qualified types
• Pointers

The syntax of these operators tries to mimic the most common appearance of const types and pointer types in C++.

Precedence

Because these are type operators, they don’t have many precedence relationship with non-type operators.

• const binds more tightly than * and can appear unparenthesized in an operand, despite being both a unary operator and having whitespace separating it.
  • This allows the syntax of a pointer to a const i32 to be const i32*, which is intended to be familiar to C++ developers.
  • Forming a const pointer type requires parentheses: const (i32*).
• All type operators bind more tightly than as so they can be used in its type operand.
  • This also allows a desirable transitive precedence with if: if condition then T* else U*.

Alternatives considered

• Alternative pointer syntaxes
• Alternative syntaxes for locals
• Make const a postfix rather than prefix operator

References

• Proposal #2006: Values, variables, and pointers