Hello,
In
http://forum.dlang.org/post/[email protected]
Adam uses findSkip as an example and especially points out the "D
idiom with is/typeof".
I'm not quite sure I understand it correctly. Please correct me
if I have misunderstood anything regarding the idiom.
findSkip:
http://dlang.org/phobos/std_algorithm_searching.html#.findSkip
bool findSkip
(alias pred = "a == b", R1, R2)
(ref R1 haystack, R2 needle)
if (isForwardRange!R1 &&
isForwardRange!R2 &&
is( [C]
typeof( [B]
binaryFun!pred( [A]
haystack.front, needle.front))));
[A]
Nothing special. findSkip's pred is passed on to binaryFun.
binaryFun's constraints thus apply to findSkip's pred.
See http://dlang.org/phobos/std_functional.html#.binaryFun
[B]
Evaluates to the function type "constructed" by binaryFun.
[C]
The is expression is true if A->B is valid "code".
It is used to convert any compiler errors to "false" (thus the
constraint wouldn't be fulfilled).
Question:
I guess that binaryFun is used in the implementation of findSkip.
The reason for using this type of idiom is to avoid "compilation
errors" to occur in the implementation when pred/R1/R2 is
"funky". It "confuses" the user.
The idiom is thus used to move errors to the call site?
"D idiom: constraint error at call site"?
