Equality and Hashing

Design for value equality and hashing in Metric Engine.

Equality Semantics

Value Equality

Two financial values are equal if:

Same numerical value
Same unit type
Same currency (for monetary values)

Approximate Equality

For floating-point values:

Configurable tolerance (default: 1e-6)
Relative vs absolute comparison
Unit-aware comparison

Hashing Strategy

class FinancialValue:
    def __hash__(self):
        return hash((
            round(self.value, 6),  # Normalized precision
            self.unit.symbol,
            self.unit.dimension
        ))

Equality Modes

Strict: Exact equality only
Approximate: Floating-point tolerant
Unit-aware: Consider unit compatibility

Use Cases

Set membership
Dictionary keys
Comparison operations
Sorting algorithms

Performance

Cached hash values
Fast path for same-object comparison
Optimized unit comparison