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digitalmars.D.learn - what's meaning of "(a) =>"

reply step8 <step7 163.com> writes:
I'm trying to study D programming
Following is code from vibe's example(web_ajax) code:
~~~~
void getDataFiltered(Fields field, string value)
{
	auto table = users.filter!((a) => value.length==0 || 
a[field]==value)().array();
	render!("createTable.dt", table)();
}
~~~~
I can't understand the expression　"(a) =>"，there is no defination 
of "a",how does this work?
thanks for help
Feb 05 2022
parent reply Stanislav Blinov <stanislav.blinov gmail.com> writes:
On Saturday, 5 February 2022 at 15:10:19 UTC, step8 wrote:

 I'm trying to study D programming
 Following is code from vibe's example(web_ajax) code:
 ~~~~
 void getDataFiltered(Fields field, string value)
 {
 	auto table = users.filter!((a) => value.length==0 || 
 a[field]==value)().array();
 	render!("createTable.dt", table)();
 }
 ~~~~
 I can't understand the expression　"(a) =>"，there is no 
 defination of "a",how does this work?
 thanks for help


`(a) => value.length==0 || a[field]==value`

is a https://dlang.org/spec/expression.html#FunctionLiteral (see 


This one is polymorphic, somewhat equivalent to defining a 
function such as

`bool func(T)(T a) { return value.length==0 || a[field]==value; }`

(assuming `value` is accessible to `func`).
Feb 05 2022
parent step8 <step7 163.com> writes:
On Saturday, 5 February 2022 at 15:17:05 UTC, Stanislav Blinov 
wrote:

 On Saturday, 5 February 2022 at 15:10:19 UTC, step8 wrote:

 I'm trying to study D programming
 Following is code from vibe's example(web_ajax) code:
 ~~~~
 void getDataFiltered(Fields field, string value)
 {
 	auto table = users.filter!((a) => value.length==0 || 
 a[field]==value)().array();
 	render!("createTable.dt", table)();
 }
 ~~~~
 I can't understand the expression　"(a) =>"，there is no 
 defination of "a",how does this work?
 thanks for help


 `(a) => value.length==0 || a[field]==value`

 is a https://dlang.org/spec/expression.html#FunctionLiteral 


 This one is polymorphic, somewhat equivalent to defining a 
 function such as

 `bool func(T)(T a) { return value.length==0 || a[field]==value; 
 }`

 (assuming `value` is accessible to `func`).


Thanks very much.I think i kind of get that now.
Feb 06 2022