Dne 5.9.2016 v 14:15 dom via Digitalmars-d-learn napsal(a):
I am about to write my own stupid and simple http client .. and i have
added a callback function that has the received content as a parameter.
class AsyncHttpGet
{
this(string host, ushort port, string path, void delegate(string)
callback )
{ ... }
}
My first attempt was to write:
auto f = new AsyncHttpGet("www.dprogramming.com", 80, "/index.php",
(string content) => {
...
});
but this is does not work because my AsyncHttpGet takes a normal
delegate and this => seems to add nothrow @nogc @safe to my delegate
type.
The correct syntax is only marginally differnt, but took me quite a
while to figure out:
( the missing arrow )
auto f = new AsyncHttpGet("www.dprogramming.com", 80, "/index.php",
(string content)
{
... // this is of type function
});
i noticed that delegates are "more powerful" than functions. once the
passed function e.g. needs to capture a value from the outside it
becomes a delegate type. I have also read that a delegate can contain
a reference to a class method bound to an instance.
int dummy = 0;
auto f = new AsyncHttpGet("www.dprogramming.com", 80, "/index.php",
(string content)
{
dummy = 1; // this is of type delegate
});
but what is the difference between a lambda (=>) and a
functions/delegates?
i think this is a major pitfall for newcomers, and should be adressed
somehow.
(string content) => { } // this is delegate which returns another
delegates {} is shorthand here for (){}
when you use => syntax you can just return expression
(string content) => content; is same as (string content) { return content; }
