How do you make a library system in PHP?

Answer 1

Assuming that "a collection of useful functions" is the intended meaning of "library," this is essentially the same process in all languages. The primary difference from an application is that a library doesn't actually do anything; it only provides tools which other programs can use. To that end, you should ensure that your functions work for as wide a variety of use-cases as is practical. However, also be careful to not make the logic overly complex to support some corner cases.

You should first decide what the central purpose of the program is, and set about writing functions (and classes, in some cases) which satisfy that purpose. This can be done in at least two ways: by detailed pre-planning, or by quickly implementing everything according to the concept in your own head.

Detailed pre-planning is the better method (for any large program, not just libraries), but some programmers have difficulty designing a program on paper rather than in code. Even if you are unable to do this at first, try writing a simple mock-up and use it as a learning experience from which to draw ideas for your design document. Then start over, using the design document as a guide and repeat this process as many times as necessary. The primary benefit of this is that you will be less likely to get tangled up in conflicting ideas for how the program should work.

Alternatively, you can just start programming by the seat of your pants. This is commonly known within the programming community as "hacking." While it is more efficient than pre-planning for smaller bits of code, you will be more likely to write ugly, confusing code as the project grows.

In both cases, of course, proper programming style is essential. Write self-documenting code as often as possible, comment where this doesn't work, and document all functions, classes, class members, and (as necessary) global variables. And make sure to test everything frequently, perhaps setting planned features as milestones, after whose initial implementation you will run all tests to ensure that the new code didn't break old code.

Finally, very large projects are often separated into modules, which are locked from modification once they are completed. If a completed module must be modified to accomodate another, you should return to the pre-planning stage to produce a new design document, ensuring that the new implementation will be compatible with all the modules which already depend on the one to be modified.