The article gets things flatly wrong from its first, ah, assertion. Asserts aren't for validation: the condition is supposed to be impossible to be false, just

The article gets things flatly wrong from its first, ah, assertion. Asserts aren't for validation: the condition is supposed to be impossible to be false, just not provable by the type system. If invalid input can come through normal operation of the program, you use a normal runtime check, not an assert.