Remainder Assignment

The %= (remainder assignment) operator is a compound assignment operator that computes the remainder of dividing the left operand by the right operand, and subsequently assigns that computed value to the left operand.

It is a syntactic shorthand equivalent to:

x = x % y

Technical Specifications

• Type Constraints: Both operands must resolve to identical integer types (e.g., int, int64, uint8). Go strictly prohibits the use of the remainder operator on floating-point (float32, float64) or complex types.
• Sign Rules: The sign of the resulting remainder always matches the sign of the dividend (the left operand). The sign of the divisor (the right operand) has no effect on the sign of the result.
• Evaluation Order: The left operand is evaluated only once during the operation.
• Runtime Panics: If the right operand evaluates to 0, the operation will trigger a runtime panic (panic: runtime error: integer divide by zero).

Syntax Visualization

// Standard positive integers
var x int = 14
x %= 4    // x evaluates to 2 (14 = 3 * 4 + 2)

// Negative dividend (result takes the sign of the dividend)
var y int = -14
y %= 4    // y evaluates to -2

// Negative divisor (divisor sign is ignored in the result)
var z int = 14
z %= -4   // z evaluates to 2

// Type mismatch (Compilation Error)
var a int32 = 10
var b int64 = 3
// a %= b // Invalid operation: mismatched types int32 and int64

Master Go with Deep Grasping Methodology!

Learn More