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.