Types with default initial values specified (from Ada 2012)

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Types with default initial values specified (from Ada 2012) [12800967]

Submitted by Alexei Odeychuk on 3/4/2016 12:00:00 AM
[ 3 votes ]

I suggest introducing an aspect that can be applied to declarations of enumeration types, discriminated union types and user-defined numeric types with the aim of specifying their default initial values in code easily. This suggestion is an extension of my previous suggestion: Types with predicates to create subtypes easily (from Ada 2012) Please see it for more details: /archive/suggestion-12564486-types-with-predicates-to-create-subtypes-easily-f Example # 1: type OK = bool [with] default true // type with true as its default initial value Example # 2: type Animals = | Tiger | Lion | Cat | Mouse | Hamster [with] default Cat type Prey = Animals with function | Mouse | Hamster -> true | _ -> false [and] default Hamster let a : Prey array = Array.zeroCreate 3 // array of 3 hamsters Remark: "[and]" or "[with]" means that the "and", "with" keywords are optional in the above-mentioned lines of code. It's not a breaking change in the language; no new keywords are needed to implement this syntax in the F# language. I think this syntax will help represent a programmer's intent in code and improve the expressiveness of the F# language.

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Posted by Jack Fox on 3/6/2016 11:41:00 AM

I suggest making the "and" and "with" keywords mandatory...I think it improves readability.

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Posted by Richard Gibson on 4/13/2016 9:56:00 AM

This would be great, especially if the F# library would come with a function similar to genericOne and we can use this as a static type constraint. That way you could write a generic function that works on any type that defines a default value.