# Naming conventions

# Table of contents

• Overview
• Details
  • Constants
  • Carbon-provided item naming
• Alternatives considered
• References

# Overview

Our naming conventions are:

• For idiomatic Carbon code:
  • UpperCamelCase will be used when the named entity cannot have a dynamically varying value. For example, functions, namespaces, or compile-time constant values.
  • lower_snake_case will be used when the named entity's value won't be known until runtime, such as for variables.
• For Carbon-provided features:
  • Keywords and type literals will use lower_snake_case.
  • Other code will use the guidelines for idiomatic Carbon code.

In other words:

We only use UpperCamelCase and lower_snake_case in naming conventions in order to minimize the variation in rules.

# Details

# Constants

Consider the following code:

package Example;

let CompileTimeConstant: i32 = 7;

fn RuntimeFunction(runtime_constant: i32);

In this example, CompileTimeConstant has a singular value (7) which is known at compile-time. As such, it uses UpperCamelCase.

On the other hand, runtime_constant may be constant within the function body, but it is assigned at runtime when RuntimeFunction is called. Its value is only known in a given runtime invocation of RuntimeFunction. As such, it uses lower_snake_case.

# Carbon-provided item naming

Carbon-provided items are split into a few categories:

• Keywords; for example, for, fn, and var.
• Type literals; for example, i<digits>, u<digits>, and f<digits>.
• Boolean type and literals; for example, bool, true, and false.
  • The separate categorization of booleans should not be taken as a rule that only booleans would use lowercase; it's just the only example right now.
• Self and Base.
• Other Carbon types; for example, Int, UInt, and String.

Note that while other Carbon types currently use UpperCamelCase, that should not be inferred to mean that future Carbon types will do the same. The leads will make decisions on future naming.

# Alternatives considered

• Other naming conventions
• Other conventions for naming Carbon types

# References

• Proposal #861: Naming conventions