var.opCmp

Three-way comparison operator for var.

Enables use of `<`, `<=`, `>`, `>=` operators between var values.

Comparison rules:

• Numeric types: Compared by numeric value with automatic type promotion. If either operand is floating-point, both are compared as double. Otherwise, integers are compared without wrap-around:
• Unsigned vs unsigned compares as ulong.
• Signed vs signed compares as long.
• Mixed signed/unsigned compares by numeric value (a negative signed value is always less than any unsigned value).
• Strings: Compared lexicographically using D's built-in string comparison.
• Booleans: false < true.
• Characters: Compared by their Unicode code point value.
• NULL: NULL is considered less than any non-NULL value. Two NULL values are equal (returns 0).
• Arrays: Compared element-by-element (lexicographic order). Shorter arrays are less than longer arrays if all elements match.
• Objects: Not directly comparable; returns 0 (equal) if same reference or both empty, otherwise comparison is undefined (returns 0).
• Mixed incompatible types: When types are incompatible for comparison (e.g., string vs array), the result is based on type tag ordering.

  Returns

  - Negative value if this < rhs
• Zero if this == rhs
• Positive value if this > rhs