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. Mixed integer/floating pairs compare exactly: the integer operand is never rounded to double (which would lose distinctions above 2^53 and break order transitivity). Two floating operands compare as double. Integer pairs compare 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