Adding my comments to Intersection Types documentation #11838
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radeusgd
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radeusgd
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Dec 11, 2024
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| > [!WARNING] | ||
| > Keep in mind that while both argument type check in method definitions and a | ||
| > 'type asserting' expression look similarly, they have slightly different behaviour. | ||
| > ``` | ||
| > f a:Float = a | ||
| > g a = a:Float | ||
| > ``` | ||
| > These two functions, while very similar, will have different behaviour when | ||
| > passed a value like the value `c` above. The function `f` will fail with | ||
| > a type error, because the visible type of `c` is just `Complex` (assuming | ||
| > the conversion to `Float` is not available in the current scope). | ||
| > However, the function `g` will accept the same value and return it as | ||
| > a `Float` value, based on the 'hidden' part of its type. |
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I want to make it clear that while the syntax is very similar, the checked argument and type-asserting expressions are actually different and behave differently in regard to the 'hidden' types.
JaroslavTulach
requested changes
Dec 12, 2024
| > used to create the intersection type is not available in the default | ||
| > conversion resolution scope. Thus it cannot be defined in the same module | ||
| > as `Complex` or `Float` types, but instead it should be defined in a separate | ||
| > module that is only imported in the place that will be constructing the multi-values. |
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That's correct and exactly as prototyped in the tests.
| - or inspect the types in a `case` expression, e.g. | ||
| ``` | ||
| case c of | ||
| f : Float -> f.sqrt |
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Does not work. Reported as
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Accepted as d1cbc8d |
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