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Assert

rascal-0.40.17

Synopsis​

An executable assertion.

Syntax​

assert Exp;

assert Exp₁ : Exp₂;

Types​

Exp₁Exp₂
boolstr

Description​

An assert statement may occur everywhere where a declaration is allowed. It has two forms:

An assert statement consists of a Boolean expression Exp₁ and an optional string expression Exp₂ that serves as a identifying message for this assertion.

When Exp₁ evaluates to false, an AssertionFailed exception is thrown.

Examples​

rascal>assert 1==2 : "is never true";
|prompt:///|(14,15,<1,14>,<1,29>): AssertionFailed("is never true")
    at $shell$(|main://$shell$|)
ok
rascal>int div(int x, int y) {
>>>>>>>  assert y != 0 : "y must be non-zero";
>>>>>>>  return x / y;
>>>>>>>}
int (int, int): function(|prompt:///|(0,81,<1,0>,<4,1>))
rascal>div(4,0);
|prompt:///|(42,20,<2,18>,<2,38>): AssertionFailed("y must be non-zero")
    at div(|prompt:///|(0,81,<1,0>,<4,1>))
    at $shell$(|prompt:///|(0,9,<1,0>,<1,9>))
ok