A Possibility for generating arbitrary T

[Seelengrab]

Currently, only a handful of data types are implemented directly in Supposition.jl. This feature intends to use the reflection capabilities provided by the compiler to generate (almost) any arbitrary T from its type.

This needs to:

• Account for throwing constructors
• Recurse for any required arguments
• Inspect which methods are actually constructor functions
  • Filter out the default constructor that just calls convert on every argument, since that would lead to quite a lot of avoidable errors
  • Currently, my thinking is that this can be done by inspecting code_typed, rejecting methods that infer as Union{} (these will throw) and only considering those that have an Expr(:new) in themselves. The reasoning for this is that any outer constructors that may want to establish invariants through checks like x < 5 || throw(ArgumentError()) are trivially circumventable by just calling the inner constructor directly (either with arguments that happen to dispatch to the inner one, or through invoke).
• Allow overriding through user defined dispatches
  • We have multiple dispatch, so allow users to hook into this at their own risk.

Shrinking-wise, this should just fall back to lexicographic shrinking, but this too should again be customizable. It may be the case that a user is fine with having the full space of possible values emerge from this Possibility, but only cares about shrinking them in a specific way.