ascription

Force grouping of ascription on underscore in scala

由 六月ゝ 毕业季﹏ 提交于 2019-12-11 15:39:25
问题 I am trying to do: MyObject.myMethod(_:MyType.myAttribute) This fails with type myAttribute is not a member of object MyObject which is correct. The problem is that I want to call myMethod on myAttribute of _:MyType , not ascribe MyType:myAttribute to _ . Can I somehow group the type ascription _:MyType ? (_:MyType).myAttribute returns type MyType => classOf(myAttribute) , which is not what I want. Edit: I changed the title and text of this post to no longer refer to this as the associativity

Why can't the type of id be specialised to (forall a. a -> a) -> (forall b. b -> b)?

由 时光怂恿深爱的人放手 提交于 2019-12-03 05:36:08
问题 Take the humble identity function in Haskell, id :: forall a. a -> a Given that Haskell supposedly supports impredicative polymorphism, it seems reasonable that I should be able to "restrict" id to the type (forall a. a -> a) -> (forall b. b -> b) via type ascription. But this doesn't work: Prelude> id :: (forall a. a -> a) -> (forall b. b -> b) <interactive>:1:1: Couldn't match expected type `b -> b' with actual type `forall a. a -> a' Expected type: (forall a. a -> a) -> b -> b Actual type:

What is type ascription?

由 半城伤御伤魂 提交于 2019-11-29 01:08:15
Several times I've used the wrong syntax, such as forgetting to use let in this example: let closure_annotated = |value: i32| -> i32 { temp: i32 = fun(5i32); temp + value + 1 }; error[E0658]: type ascription is experimental (see issue #23416) --> src/main.rs:3:9 | 3 | temp: i32 = fun(5i32); | ^^^^^^^^^ I know that this problem is solved by using let , but what is "type ascription" and what is its use? I found issue #23416 and the feature gate for type ascription , but I could not understand what "type ascription" is or what is its purpose. Francis Gagné Type ascription is the ability to

What is type ascription?

由 旧城冷巷雨未停 提交于 2019-11-27 15:38:39
问题 Several times I've used the wrong syntax, such as forgetting to use let in this example: let closure_annotated = |value: i32| -> i32 { temp: i32 = fun(5i32); temp + value + 1 }; error[E0658]: type ascription is experimental (see issue #23416) --> src/main.rs:3:9 | 3 | temp: i32 = fun(5i32); | ^^^^^^^^^ I know that this problem is solved by using let , but what is "type ascription" and what is its use? I found issue #23416 and the feature gate for type ascription, but I could not understand

What is the purpose of type ascriptions in Scala?

由 此生再无相见时 提交于 2019-11-26 03:51:21
问题 There\'s not much info in the spec on what type ascription is, and there certainly isn\'t anything in there about the purpose for it. Other than \"making passing varargs work\", what would I use type ascription for? Below is some scala REPL for the syntax and effects of using it. scala> val s = \"Dave\" s: java.lang.String = Dave scala> val p = s:Object p: java.lang.Object = Dave scala> p.length <console>:7: error: value length is not a member of java.lang.Object p.length ^ scala> p.getClass
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