Difference between revisions of "DIP39"
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== Details == | == Details == | ||
Suppose we have a function that takes an input by ref: | Suppose we have a function that takes an input by ref: | ||
| + | <syntaxhighlight lang="d"> | ||
T2 fun(ref T a); | T2 fun(ref T a); | ||
| − | We can use it as before with an lvalue | + | </syntaxhighlight> |
| − | fun( | + | We can use it as before with an lvalue LV (backwards compatible): |
| − | We can use it with an rvalue | + | <syntaxhighlight lang="d"> |
| + | fun(LV); | ||
| + | </syntaxhighlight> | ||
| + | We can use it with an rvalue RV 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'. | 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( | + | fun(RV^); |
| − | |||
| − | |||
| − | |||
== Alternative symbols for call site rvalue annotation == | == Alternative symbols for call site rvalue annotation == | ||
Revision as of 00:34, 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 LV (backwards compatible):
fun(LV);
We can use it with an rvalue RV 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(RV^);
Alternative symbols for call site rvalue annotation
- fun(r^);//proposed postfix annotation, compatible with left-to-right pipelines in D: [1,2].sort.map!fun.uniq
- 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.
