Difference between revisions of "DIP39"
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* no call site ref annotation when input ref argument is already an lvalue (different from C#), for backwards compatibility (and making it less verbose) | * no call site ref annotation when input ref argument is already an lvalue (different from C#), for backwards compatibility (and making it less verbose) | ||
* compatible with UFCS | * compatible with UFCS | ||
| + | |||
| + | == Details == | ||
| + | Suppose we have a function that takes an input by ref: | ||
| + | T2 fun(ref T a); | ||
| + | We can use it as before with an lvalue x (backwards compatible): | ||
| + | fun(x); | ||
| + | We can use it with an rvalue r and a call site annotation indicating to convert the rvalue to an lvalue via a temporary: | ||
| + | I propose the yet unused symbol '^' to denote this (note, it is used in some C++ extensions but that's irrelevant), although there are alternatives, see section: 'alternative symbols for call site rvalue annotation'. | ||
| + | |||
| + | |||
| + | fun(r^); | ||
| + | |||
| + | |||
| + | |||
| + | |||
| + | == Alternative symbols for call site rvalue annotation == | ||
| + | fun(r^);//proposed postfix annotation | ||
| + | fun(^r);//prefix annotation is compatible with '&' location wrt argument | ||
| + | fun(ref r);//reminds of C# call site annotation | ||
| + | fun(r@);//# has UDA meaning in D, but that could be made unambiguous | ||
| + | fun(r#); //# has a special line reordering meaning in D, but that could be made unambiguous | ||
== Copyright == | == Copyright == | ||
Revision as of 00:29, 11 May 2013
Contents
DIP 39: Safe rvalue references: compatible with DIP38, backwards compatible, safe against ref/nonref code evolution.
| Title: | Safe rvalue references: compatible with DIP38, backwards compatible, safe against ref/nonref code evolution. |
|---|---|
| DIP: | 39 |
| Version: | 1 |
| Status: | Draft |
| Created: | 2013-05-10 |
| Last Modified: | 2013-05-10 |
| Author: | Timothee Cour |
| Links: |
Abstract
We propose to introduce rvalue references that are:
- safe: guarantees memory safety so that references will always point to valid memory.
- compatible with DIP38: can use same inref/outref internal compiler annotation for input references that can be returned by ref by a function.
- backwards compatible: current valid D code will continue to work without change. In addition, additional code becomes valid with call site rvalue ref annotation.
- safe against ref/nonref code evolution: call site rvalue ref compulsory annotation turns ref/nonref changes into compile errors instead of silently changing code behavior.
- both const ref or ref can be used with rvalue refs (more flexible than C++)
- no call site ref annotation when input ref argument is already an lvalue (different from C#), for backwards compatibility (and making it less verbose)
- compatible with UFCS
Details
Suppose we have a function that takes an input by ref: T2 fun(ref T a); We can use it as before with an lvalue x (backwards compatible): fun(x); We can use it with an rvalue r and a call site annotation indicating to convert the rvalue to an lvalue via a temporary: I propose the yet unused symbol '^' to denote this (note, it is used in some C++ extensions but that's irrelevant), although there are alternatives, see section: 'alternative symbols for call site rvalue annotation'.
fun(r^);
== Alternative symbols for call site rvalue annotation ==
fun(r^);//proposed postfix annotation fun(^r);//prefix annotation is compatible with '&' location wrt argument fun(ref r);//reminds of C# call site annotation fun(r@);//# has UDA meaning in D, but that could be made unambiguous fun(r#); //# has a special line reordering meaning in D, but that could be made unambiguous
Copyright
This document has been placed in the Public Domain.
