Documentation for infix
.= assembled from the following types:
Calls the right-side method on the value in the left-side container, replacing the resulting value in the left-side container.
In most cases, this behaves identically to the postfix mutator, but the precedence is lower:
my = -5;say ++.=abs;# OUTPUT: «6␤»
say ++ .= abs;# OUTPUT: «Cannot modify an immutable Int␤# in block <unit> at <tmp> line 1␤␤»