Structural types

[DartBot]

This issue was originally filed by [email protected]

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What would you like to see instead?

I really like the idea of Go interfaces. (Classes do not have to declare what interfaces they support. An interface is a set of methods. Any class that has those methods implements the interface.)

A lot of type checking in Dart is done at runtime anyways. It would be nice if a language user could take an advantage of it. The type system could allow expressing properties that are not nominal and static, but more like structural runtime asserts.

Please provide any additional information below.

Using an example given by Miško Hevry in https://www.youtube.com/watch?v=lGdnh8QSPPk while introducing AtScript [1] @­15:00, I'd like to declare a type CssSelector which would be satisfied by anything of type String if the string matches a given Regexp.

Even though those properties are not static, an IDE could still take some limited advantage of it for code completion, during debugging and so on.

Related issue "Is the Dart type system is nominal?" #­7639

[1] https://docs.google.com/document/d/11YUzC-1d0V1-Q3V0fQ7KSit97HnZoKVygDxpWzEYW0U/edit

[lrhn]

Added Area-Language, Triaged labels.

[gbracha]

We are not about to do major surgery on the Dart type system. It's mostly nominal, with the usual structural exceptions around functions and generics.

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Set owner to @gbracha.
Added NotPlanned label.

[DartBot]

This comment was originally written by [email protected]

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I just found this request is somewhat similar to Issue #3049 "Contracts". If we get that instead, I'd be happy too.