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digitalmars.D.learn - Setting a list of values

reply Joel <joelcnz gmail.com> writes:
This has no effect:
_bars.each!(a => { a._plots.fillColor = Color(255, 180, 0); });

I tried putting ..each!((ref a) =>.. with no difference

This works:
foreach(b; _bars) {
	b._plots.fillColor = Color(255, 180, 0);
}
Apr 30 2016
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 04/30/2016 10:05 PM, Joel wrote:
 This has no effect:
 _bars.each!(a => { a._plots.fillColor = Color(255, 180, 0); });
This is a common issue especially for people who know lambdas from other languages. :) Your lambda does not do any work. Rather, your lambda returns another lambda, which is promptly ignored: import std.stdio; import std.algorithm; void main() { auto arr = [ 1, 2 ]; arr.each!(a => { writeln(a); }); // returns lambda for each a } The lambda that 'each' takes above is "given a, produce this lambda". . To do the intended work, you need to remove the curly braces (and the semicolon): arr.each!(a => writeln(a)); Or, you could insert empty () to call the returned lambda but that would completely be extra work in this case: arr.each!(a => { writeln(a); }()); Ali
Apr 30 2016
next sibling parent Marc =?UTF-8?B?U2Now7x0eg==?= <schuetzm gmx.net> writes:
On Sunday, 1 May 2016 at 05:42:00 UTC, Ali Çehreli wrote:
 On 04/30/2016 10:05 PM, Joel wrote:
 This has no effect:
 _bars.each!(a => { a._plots.fillColor = Color(255, 180, 0);
}); This is a common issue especially for people who know lambdas from other languages. :) Your lambda does not do any work. Rather, your lambda returns another lambda, which is promptly ignored: import std.stdio; import std.algorithm; void main() { auto arr = [ 1, 2 ]; arr.each!(a => { writeln(a); }); // returns lambda for each a } The lambda that 'each' takes above is "given a, produce this lambda". . To do the intended work, you need to remove the curly braces (and the semicolon): arr.each!(a => writeln(a)); Or, you could insert empty () to call the returned lambda but that would completely be extra work in this case: arr.each!(a => { writeln(a); }());
Or, remove the arrow: arr.each!((a) { writeln(a); });
May 01 2016
prev sibling next sibling parent reply Xinok <xinok live.com> writes:
On Sunday, 1 May 2016 at 05:42:00 UTC, Ali Çehreli wrote:
 On 04/30/2016 10:05 PM, Joel wrote:
 This has no effect:
 _bars.each!(a => { a._plots.fillColor = Color(255, 180, 0);
}); This is a common issue especially for people who know lambdas from other languages. :) Your lambda does not do any work. Rather, your lambda returns another lambda, which is promptly ignored:
Those are some discrete semantics. I know D pretty well and even I didn't see the problem initially. Anybody else think it's worth adding a warning to the compiler for this specific case? If this is the user's intended behavior, then they can rewrite it like this to be explicit and disable the warning: _bars.each!(a => (){ a._plots.fillColor = Color(255, 180, 0); }); // ^^ add empty parenthesis before the curly brace
May 01 2016
parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 05/01/2016 12:54 PM, Xinok wrote:
 On Sunday, 1 May 2016 at 05:42:00 UTC, Ali Çehreli wrote:
 On 04/30/2016 10:05 PM, Joel wrote:
 This has no effect:
 _bars.each!(a => { a._plots.fillColor = Color(255, 180, 0);
}); This is a common issue especially for people who know lambdas from other languages. :) Your lambda does not do any work. Rather, your lambda returns another lambda, which is promptly ignored:
Those are some discrete semantics. I know D pretty well and even I didn't see the problem initially. Anybody else think it's worth adding a warning to the compiler for this specific case?
A warning would be great but I don't see how it can cover all cases. A special warning for std.algorithm.each might work but this exact issue appeared on the main thread just a few minutes ago: http://forum.dlang.org/post/qsayoktyffczskrnmgxu forum.dlang.org alias funType = void function(int x); funType fun = (x) => { assert(x); }; // cannot return non-void from void function Ali
May 02 2016
parent reply Marc =?UTF-8?B?U2Now7x0eg==?= <schuetzm gmx.net> writes:
On Monday, 2 May 2016 at 08:46:31 UTC, Ali Çehreli wrote:
 On 05/01/2016 12:54 PM, Xinok wrote:
 On Sunday, 1 May 2016 at 05:42:00 UTC, Ali Çehreli wrote:
 On 04/30/2016 10:05 PM, Joel wrote:
 This has no effect:
 _bars.each!(a => { a._plots.fillColor = Color(255, 180, 0);
}); This is a common issue especially for people who know
lambdas from
 other languages. :)

 Your lambda does not do any work. Rather, your lambda
returns another
 lambda, which is promptly ignored:
Those are some discrete semantics. I know D pretty well and
even I
 didn't see the problem initially. Anybody else think it's
worth adding a
 warning to the compiler for this specific case?
A warning would be great but I don't see how it can cover all cases. A special warning for std.algorithm.each might work but this exact issue appeared on the main thread just a few minutes ago: http://forum.dlang.org/post/qsayoktyffczskrnmgxu forum.dlang.org alias funType = void function(int x); funType fun = (x) => { assert(x); }; // cannot return non-void from void function Ali
Warning (better: disallowing altogether) about `=>` directly followed by `{` should be enough to cover all cases. To express that you really want a lambda returning a lambda, it can be rewritten either as: (x) => () { assert(x); } or as: (x) => ({ assert(x); }) This check can be done purely by looking at the tokens. Should we someday introduce tuples with `{}`, the check needs to be done after the node starting with `{` has been parsed to distinguish between delegate and tuple literals.
May 02 2016
next sibling parent reply sigod <sigod.mail gmail.com> writes:
On Monday, 2 May 2016 at 10:15:04 UTC, Marc Schütz wrote:
 On Monday, 2 May 2016 at 08:46:31 UTC, Ali Çehreli wrote:
 [...]
Warning (better: disallowing altogether) about `=>` directly followed by `{` should be enough to cover all cases. To express that you really want a lambda returning a lambda, it can be rewritten either as: (x) => () { assert(x); } or as: (x) => ({ assert(x); }) This check can be done purely by looking at the tokens. Should we someday introduce tuples with `{}`, the check needs to be done after the node starting with `{` has been parsed to distinguish between delegate and tuple literals.
It's good idea. I myself stumbled into this before.
May 02 2016
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 5/2/16 6:00 PM, sigod wrote:
 On Monday, 2 May 2016 at 10:15:04 UTC, Marc Schütz wrote:
 On Monday, 2 May 2016 at 08:46:31 UTC, Ali Çehreli wrote:
 [...]
Warning (better: disallowing altogether) about `=>` directly followed by `{` should be enough to cover all cases. To express that you really want a lambda returning a lambda, it can be rewritten either as: (x) => () { assert(x); } or as: (x) => ({ assert(x); }) This check can be done purely by looking at the tokens. Should we someday introduce tuples with `{}`, the check needs to be done after the node starting with `{` has been parsed to distinguish between delegate and tuple literals.
It's good idea. I myself stumbled into this before.
Agree. -Steve
May 02 2016
parent sigod <sigod.mail gmail.com> writes:
On Monday, 2 May 2016 at 23:41:39 UTC, Steven Schveighoffer wrote:
 On 5/2/16 6:00 PM, sigod wrote:
 On Monday, 2 May 2016 at 10:15:04 UTC, Marc Schütz wrote:
 On Monday, 2 May 2016 at 08:46:31 UTC, Ali Çehreli wrote:
 [...]
Warning (better: disallowing altogether) about `=>` directly followed by `{` should be enough to cover all cases. To express that you really want a lambda returning a lambda, it can be rewritten either as: (x) => () { assert(x); } or as: (x) => ({ assert(x); }) This check can be done purely by looking at the tokens. Should we someday introduce tuples with `{}`, the check needs to be done after the node starting with `{` has been parsed to distinguish between delegate and tuple literals.
It's good idea. I myself stumbled into this before.
Agree. -Steve
https://issues.dlang.org/show_bug.cgi?id=16001
May 07 2016
prev sibling parent Brian Schott <briancschott gmail.com> writes:
On Monday, 2 May 2016 at 10:15:04 UTC, Marc Schütz wrote:
 This check can be done purely by looking at the tokens.
In other words it's trivial for D-Scanner to warn about this. https://github.com/Hackerpilot/Dscanner/issues/341
May 07 2016
prev sibling parent reply Joel <joelcnz gmail.com> writes:
On Sunday, 1 May 2016 at 05:42:00 UTC, Ali Çehreli wrote:
 On 04/30/2016 10:05 PM, Joel wrote:
 This has no effect:
 _bars.each!(a => { a._plots.fillColor = Color(255, 180, 0);
}); This is a common issue especially for people who know lambdas from other languages. :) Your lambda does not do any work. Rather, your lambda returns another lambda, which is promptly ignored: import std.stdio; import std.algorithm; void main() { auto arr = [ 1, 2 ]; arr.each!(a => { writeln(a); }); // returns lambda for each a } The lambda that 'each' takes above is "given a, produce this lambda". . To do the intended work, you need to remove the curly braces (and the semicolon): arr.each!(a => writeln(a)); Or, you could insert empty () to call the returned lambda but that would completely be extra work in this case: arr.each!(a => { writeln(a); }()); Ali
This seems to work the best: arr.each!(a => { writeln(a); }());
May 03 2016
parent sigod <sigod.mail gmail.com> writes:
On Wednesday, 4 May 2016 at 04:56:54 UTC, Joel wrote:
 On Sunday, 1 May 2016 at 05:42:00 UTC, Ali Çehreli wrote:
 [...]
This seems to work the best: arr.each!(a => { writeln(a); }());
And the ugliest. And probably slowest.
May 07 2016