digitalmars.D.learn - What is the corect behavour for lazy in foreach variadic template
- Sean Campbell (23/23) Sep 25 2015 Take the following code for example
- =?UTF-8?Q?Ali_=c3=87ehreli?= (17/21) Sep 25 2015 I don't think that syntax is implemented. It looks valid to me though.
- Artur Skawina via Digitalmars-d-learn (14/15) Sep 25 2015 His original code does work (`foreach` evaluates `args[N]` and
- =?UTF-8?Q?Ali_=c3=87ehreli?= (3/18) Sep 25 2015 Awesome! :)
Take the following code for example module test; import std.stdio; void test(T...)(lazy T args) { foreach(arg;args) //bar is invoked here { writeln("about to process arg"); writefln("processing arg %s",arg); //but it should be invoked here, right? } } int bar() { writeln("bar invoked"); return 1; } void main() { test(bar()); } shouldn't bar be evaluated when writefln is called, not at the start of the loop.
Sep 25 2015
On 09/25/2015 05:56 AM, Sean Campbell wrote:Take the following code for example module test; import std.stdio; void test(T...)(lazy T args)I don't think that syntax is implemented. It looks valid to me though. There are many qualifier combinations that the compiler is silent about. I think this is one of those cases. Are you familiar with the 'Lazy variadic functions' feature? It works but as far as I understand it, all arguments must be of the same type: http://dlang.org/function.html As long as all 'int's are acceptable, the change to your code would be void test(int delegate()[] args...) There is the following related discussion: http://forum.dlang.org/post/ppcnyjpzcfptkoxkdrtk forum.dlang.org I haven't tried it from but John Colvin's solution there probably has the same issue. Perhaps we need an enhancement that either works in your original code or lazy variadics to support something like the following: void test(T...)(T delegate()[] args...) Ali
Sep 25 2015
On 09/25/15 17:47, Ali Çehreli via Digitalmars-d-learn wrote:Perhaps we need an enhancement that either works in your original code [...]His original code does work (`foreach` evaluates `args[N]` and assigns the result to `arg`). If he wanted to delay the evaluation, he would have written it like this: void test(T...)(lazy T args) { foreach(I, _; typeof(args)) { writeln("about to process arg"); writefln("processing arg %s",args[I]); } } artur
Sep 25 2015
On 09/25/2015 09:38 AM, Artur Skawina via Digitalmars-d-learn wrote:On 09/25/15 17:47, Ali Çehreli via Digitalmars-d-learn wrote:Awesome! :) AliPerhaps we need an enhancement that either works in your original code [...]His original code does work (`foreach` evaluates `args[N]` and assigns the result to `arg`). If he wanted to delay the evaluation, he would have written it like this: void test(T...)(lazy T args) { foreach(I, _; typeof(args)) { writeln("about to process arg"); writefln("processing arg %s",args[I]); } } artur
Sep 25 2015