>From the expansion we can see that if-let determine the result based on
the second param, in your case: {:key2 "a string"}, not the local binding
you assumed(key1), and
I think it is reasonable, for example, if we have the following code:
(if-let [{key1 key2} {:key2 "a string"}]
true
false))
Should if-let determine the result based on key1? key2? IMO {key1 key2} in
a whole is more reaonable. And {key1 key2} == {:key2 "a string"}, then the
result is true.
On 13-1-30 下午4:51, "Mimmo Cosenza" <[email protected]> wrote:
>Hi all,
>I'm a little bit confused about the semantic of if-let macro.
>
>Suppose to call it as follows with map destructoring:
>
>(if-let [{key1 :key1} {:key2 "a string"}]
> true
> false))
>
>It returns true.
>
>But,
>
>(let [{key1 :key1} {:key2 "a string"}]
> (if key1
> true
> false))
>
>returns false.
>
>
>The macro expansion of the former explains why
>
>(macroexpand-1 '(if-let [{key1 :key1} {:key2 "a string"}] true false))
>
>returns
>(clojure.core/let [temp__3971__auto__ {:key2 "a string"}] (if
>temp__3971__auto__ (clojure.core/let [{key1 :key1} temp__3971__auto__]
>true) false))
>
>the consequence, IMHO, is that I would never suggest to use map
>restructuring inside and if-let binding, because the syntax let me think
>the result its the opposite of its semantic,
>
>Am I completely wrong?
>
>mimmo
>
>
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