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Informations about the package later
This rigorously tested fully-typed library just works. It neither defines nor throws any exceptions.
Install
composer require sanmai/laterThe latest version requires PHP 7.4 or greater.
Use
To use this pattern you need a generator function, yielding a single item of type you want to produce lazily. Pass it to later(), a static wrapper returning a Deferred object:
For example:
And then call get() when needed, as many times as needed:
Using a generator instead of a traditional callback comes with a major benefit: any generator is guaranteed by the language to be used exactly once. You can be sure that it won't be called twice.
But that's not all: read on.
No Callbacks Required
Making a closure generator on the spot isn't always convenient. And not to say these closures are much different from all-too-familiar callbacks. Not at all different from the looks of them.
The power of this pattern is in its ability to make use of any function, previously returning a single value, without any need for any additional callbacks or closures.
Consider this diff:
After adding Later\lazy to the mix:
We can see, this simple, single-line, change in the original method freed our program from creating things it may not need, postponing this process until the last moment, while also avoiding any use of callbacks.
Type Transparency
The library is completely typed. PHPStan, Psalm, and Phan are all routinely supported.
To exploit this capability it is recommended to declare a variable holding this object as \Later\Interfaces\Deferred<Type>.
In this example it will be Deferred<DeepThought>:
Following this approach, a static analyzer will be able to understand what is called, and what is returned.
Eager Execution
What if a program calls for Deferred object, but lazy evaluation is not required? For example, because a result is already available being loaded from a cache.
No problem, there's a function for this:
This deferred-but-not-deferred object implements the same interface, and can be used anywhere where a normal Deferred object would go.
Writing Tests
The underlying Deferred object is fairly lax about input types. It will be happy to accept any iterable, not just generators.
This makes it super easy to use in mocks:
Yet for constant and already-known answers best to use a non-deferred variant:
And that's it. No need to go through loops assembling closures and whatnot.
If nothing else, one can make a common mock for it:
API Overview
| Method | Takes | Returns |
|---|---|---|
Later\lazy() |
iterable<T> |
\Later\Interfaces\Deferred<T> |
Later\later() |
A generator callback for T |
\Later\Interfaces\Deferred<T> |
Later\now() |
T |
\Later\Interfaces\Deferred<T> |
