Editing Postcondition (section)

==Eiffel example==

The following example written in [[Eiffel (programming language)|Eiffel]] sets the value of a class attribute <code>hour</code> based on a caller-provided argument <code>a_hour</code>. The postcondition follows the keyword <code>ensure</code>. In this example, the postcondition guarantees, in cases in which the precondition holds (i.e., when <code>a_hour</code> represents a valid hour of the day), that after the execution of <code>set_hour</code>, the class attribute <code>hour</code> will have the same value as <code>a_hour</code>. The tag "<code>hour_set:</code>" describes this postcondition clause and serves to identify it in case of a runtime postcondition violation.

<syntaxhighlight lang="eiffel">
    set_hour (a_hour: INTEGER)
            -- Set `hour' to `a_hour'
        require
            valid_argument: 0 <= a_hour and a_hour <= 23
        do
            hour := a_hour
        ensure
            hour_set: hour = a_hour
        end
</syntaxhighlight>