A minimal package to expose an interface for reasoning about and controlling the mutability of indexable containers, via:
issettable(x) returns a Bool indicating whether setindex! works on x.freeze(x) returns a container with the values contained within x that cannot be mutated via setindex!.thaw(x) is the reverse of freeze, returning a container with the values contained with x that can be mutated via setindex!.In the general case, the above might require copying the contents of x, but in practice we
expect the Julia compiler to become good at reasoning about the lifetime of objects via escape
analysis (as it can already do for structs).
NOTE: The current implementation here for AbstractArray might be unsound because it does not perform defensive copying! This package provides interface guarantees around setindex! only - actual values may mutate if the underlying data structures are accessed directly. It may be useful for experimentation or preventing some varieties of bugs.
See also Base.Experimental.Const in Julia 1.3 onwards, and the ArrayInterface.jl package.