70s first tutorial: getCurrentDate(). Piece of Cake. We are in the 20s Time is global no more
Problems
Coupling
Fragile Tests
Timezone Problems
Solutions
- Use Dependency injection to decouple time source.
Sample Code
Wrong
var today = new Date();
Right
var ouagadougou = new Location();
var today = myTimeSource.currentDateIn(ouagadougou);
function testTimePasses() {
$mockTime = new MockedDate(new Date(1,1,2021));
myDomainSystem = new TimeSystem(new MockedTime());
// ..
$mockTime.moveDateTo(new Date(1,1,2022));
// ...
this.assert(10, myDomainSystem.accuredInterests());
}
Detection
We should forbid global functions policies. We need to couple to accidental and pluggable time sources.
Conclusion
Date.today() , Time.now()
, and other global system calls are coupling smell.
Since tests must be in full environmental control. We should easily set up time, moved it back and forth etc.
Date and Time classes should only create immutable instances. It is not their responsibility to give the actual time. This violates Single Responsibility Principle.
The passage of time is always scorned by programmers. This makes objects mutable and designs poor and coupled.
Relations
More info
Tags
- Globals
In programming, the hard part isn't solving problems, but deciding what problems to solve.
Paul Graham
This article is part of the CodeSmell Series.