Define hash for PointSpace and DiracSpace

[jishnub]

Space defines == generically in src/Space.jl:165:

==(A::Space,B::Space) = spacescompatible(A,B) && domain(A) == domain(B)

but there is no matching hash, so spaces fall back to the identity-based default. Two equal-valued PointSpaces hash differently, which silently breaks Set and Dict:

julia> PointSpace(1:2) == PointSpace(1:2)
true

julia> hash(PointSpace(1:2)) == hash(PointSpace(1:2))
false

julia> Set([PointSpace(1:2), PointSpace(3:4)]) == Set([PointSpace(3:4), PointSpace(1:2)])
false

For PointSpace and DiracSpace, spacescompatible reduces to comparing the sorted points, and domain is derived from that same field, so hashing the points reproduces == exactly. The type is mixed into the hash so PointSpace(1:2) and DiracSpace(1:2) don't collide — they are not ==, since spacescompatible is only defined within each type.

Note == compares points numerically, so PointSpace([1,2]) == PointSpace([1.0,2.0]); the hash agrees, since Julia hashes numerically-equal numbers identically. Covered in the tests.

Scope

This fixes only the two types where the failure is demonstrated. Every other Space subtype still hashes by identity — == is generic but hash is not. A generic hash(::Space, ::UInt) can't be derived safely, because spacescompatible is an arbitrary user-overridable predicate and nothing constrains which fields it consults. Fixing the rest means a hash alongside each spacescompatible, which seems worth a separate issue rather than bundling here.

Full test suite passes locally (219 passed, 1 pre-existing broken, 0 failures).

🤖 Generated with Claude Code

https://claude.ai/code/session_01DZeBMyvW7qYiDfC7Tkb1vT

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.10%. Comparing base (023b1a4) to head (42a1b10).
⚠️ Report is 47 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #698      +/-   ##
==========================================
- Coverage   75.20%   74.10%   -1.11%     
==========================================
  Files          79       81       +2     
  Lines        8445     8603     +158     
==========================================
+ Hits         6351     6375      +24     
- Misses       2094     2228     +134     

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