Assignment Expressions

The expression syntax, semantics, associativity and precedence are quite identical to the corresponding C and C++ expressions except that the simple assignment operator in OQL is := instead of = in C or C++. The left operand must be a left value. A left value is an OQL entity which is assignable: for instance any identifier or a valid path expression.
When the assignment is simple and when the left value is an identifier, no type checking on the right operand is done. For instance, x := 10 and x := "hello" are always valid expressions. In the case of the left value is a path expression, the OQL interpreter checks that the type of the second operand matches the expected type of the first one. For instance if p denotes a Person instance, p->age := 32 is certainly valid while p->age := "hello" raises a type check error.
When the assignment is combined with another operation (for instance, the -= operator), the left operand must be initialized and the interpreter checks that the left and right operand can be combined through the other operator.

For instance, the following constructs are valid:

a := 10;
a -= 20;

a := "hello";
a += " world";

p := first(select Person);
p.name := "johnny";

first(select Person.age = 0).name := "baby";

while these ones produce errors:

a := "hello";
a -= 20; // raises the error: operation 'string + integer' is not valid

a := list(1, 2);
a *= 2; // raises the error: operation 'list * integer' is not valid

unset b;
b += 20; // raises the error: uninitialized identifier 'b'

p := first(select Person);
p.age := "baby"; // raises the error: integer expected, got string

General Information
Operators	:=
	*=
	/=
	%=
	+=
	-=
	«=
	»=
	&=
	|=
	^=
Type	binary
Syntaxes	lvalue := expr
	lvalue *= expr
	lvalue /= expr
	lvalue %= expr
	lvalue += expr
	lvalue -= expr
	lvalue «= expr
	lvalue »= expr
	lvalue &= expr
	lvalue |= expr
	lvalue ^= expr
Commutative	no
Operand Types	leftvalue on the left side and any type on the right side
Result Type	the type of the right operand
Functions	perform an operation and assignment

Expression Examples
expression	result
a := 24	24
a += 12	36
a /= 2	18
a ^= 100	118
first(select Person).age := 38	38
"hello" := 4	raises an error (i.e. "hello" is not a leftvalue)
8 := 5	raises an error (i.e. 8 is not a leftvalue)
unset a; a += 20	raises an error (i.e. uninitialized identifier)