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`map` forgets its shrinker

See original GitHub issue

For example:

Gen.string().shrinker != null
Gen.string().map { it }.shrinker() == null

This means we don’t get a free shrinker when combining Gens. Moreover, it is surprising behaviour for users since it violates the functor law for map.

If it cannot be implemented without breaking covariance, then I think shrinker() should be removed from the Gen interface, and Gen should go back to being covariant.

Issue Analytics

State:
Created 5 years ago
Reactions:3
Comments:24 (14 by maintainers)

Top GitHub Comments

1reaction

sksamuelcommented, Nov 16, 2018

Yes that’s one solution I suppose.

If I want to write a custom generator for strings, then I can either lose shrinker support, wrap the type in a data class, or have an overloaded forAll that accepts a specific shrinker. Out of those, I don’t think there’s much to choose between the last two, in that they’re both not ideal, but I do think they’re probably both better than the current situation.

0reactions

LeoColmancommented, Dec 27, 2019

Closed as per #1135