carbon-lang/proposals/p1382.md

Rename me -> self

Pull request

Table of contents

• Problem
• Background
• Proposal
• Rationale
• Alternatives considered
  • Don't change anything
  • this

Problem

We've tried the fn MethodName[me: Self]() syntax for a while, and from our experience the brevity of me is not worth doing something novel in this space. We have found that me doesn't read well in practice.

Background

The current method syntax, including these choices, was decided in questions-for-leads issue #494: Method syntax and implemented in proposal #722: Nominal classes and methods.

Looking at other languages that use reserved word for the receiver value:

When	Language	Receiver when accessing members	Receiver value	Receiver type
1983	C++	implicit	this	---
1991	Python	explicit	self	---
1995	Java	implicit	this	---
1995	JavaScript	explicit	this	---
2000	C#	implicit	this	---
2009	Go	explicit	(see below)	---
2010	Rust	explicit	self	Self
2011	Kotlin	implicit	this	---
2012	TypeScript	explicit	this	this
2014	Swift	implicit	self	Self
previously	Carbon	explicit	me	Self
proposed	Carbon	explicit	self	Self

In detail:

• C++ uses this for address of the receiver value. C++23 includes an explicit this facility. Examples in the proposal frequently use self as the name of the parameter, and Self as its type.
• Swift uses self for the receiver value. and Self for its type.
• Rust uses self for the receiver value and Self for its type.
• C# uses this for a reference to the receiver value.
• Python as a convention uses self for the receiver value, but it's almost universally followed.
• Go conventionally uses an abbreviation of the type name.

Some history about the use of self in programming languages is documented in this StackOverflow answer, including that self is also used in Smalltalk, Modula-3, Delphi/Object Pascal, and Objective-C.

Proposal

Use self instead of me to be consistent with Swift and Rust.

Rationale

This is consistent with Carbon's goal to make Code that is easy to read, understand, and write by choosing a keyword for this role that is less surprising to users.

Alternatives considered

Don't change anything

We could stay with the status quo, which has the benefit that me is shorter than self. There are two considerations:

• For accessing members of the current object, the chart in the background section shows plenty of precedent for requiring a 4 character explicit keyword.
• We would also like to reduce ceremony when declaring the signature of a method. For this concern, both me: Self and addr me: Self* are already longer than what other languages use in practice. It would probably be better to solve this problem with a shortcut approach like Rust (1, 2), where &self is short for self: &Self and &mut self is short for self: &mut Self.

this

We could also switch to this, primarily to benefit C++ users. This had a few disadvantages:

• We are worried that it frequently not being a pointer would be surprising to those C++ users.
• As noted in the background section, C++23 code using explicit this frequently uses the name self.
• We view it as an advantage to use the same spelling for the variable self as for the type Self, and while this might make an acceptable name for the object parameter, Self is much more strongly established as the name for the current class, for example in PL research, and there is no precedent for a type named This.