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The right shift assignment operator (>>=) is a compound assignment operator that performs a bitwise arithmetic right shift on the left operand by the number of bit positions specified by the right operand, and subsequently assigns the result back to the left operand.

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Syntax

variable >>= numberOfBits;
This expression is semantically equivalent to: 
variable = variable >> numberOfBits;

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Operational Mechanics

  1. Type Constraint: Both operands must be of type int.
  2. Bitwise Shift: The binary representation of variable is shifted to the right by numberOfBits.
  3. Sign Extension: Dart uses arithmetic shifting. The empty bit positions created on the left (most significant bits) are filled with the value of the original sign bit:
    • If the number is positive (sign bit 0), 0s are shifted in.
    • If the number is negative (sign bit 1), 1s are shifted in to preserve the sign in two’s complement representation.
  4. Truncation: Bits shifted off the right end (least significant bits) are discarded.
  5. Assignment: The resulting integer value is stored in variable.

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Examples

Positive Integer Shift Shifting a positive integer fills the most significant bits with 0. 
void main() {
  int x = 12;      // Binary: 0000 ... 1100
  
  x >>= 2;         // Shift right by 2 positions
                   // Binary: 0000 ... 0011
                   
  print(x);        // Output: 3
}
Negative Integer Shift (Sign Extension) Shifting a negative integer fills the most significant bits with 1. 
void main() {
  int y = -8;      // Binary (64-bit two's complement): 1111 ... 1000
  
  y >>= 1;         // Shift right by 1 position
                   // Binary: 1111 ... 1100
                   
  print(y);        // Output: -4
}
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