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Jesse Phillips
Jesse Phillips

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What is in an API?

I find that people assign a lot more requirements to being an application programming interface than exist, like having a REST endpoint or being public. Similar to how people expect more from continuous integration.

To bring clarity in the purpose of the term 'API' I need to bring in another, ABI. You don't hear much about Application Binary Interface very often, how frequently do you program in binary?

The binary interface is something critical for compilers and virtual machines. In the C++ world the ABI is not a defined standard so compilers will define their own. This means libraries compiled in on compiler are no usable in another. D facilitates C++ integration by choosing to implement the ABI for the dominant compiler of the platform. For its own libraries D has not defined being ABI compatible across compiler releases, this means libraries need recompiled for each compiler version, potentially.

I hope that this helps to create some perspective on what is an API. In contrast to the ABI the Application Programming Interface is what the application programmer writes their code against. At the simplest level this is your function signatures.

The compiler has freedom in how it expects this signature is stored for calling. Is the left argument first on the stack or last?


With this definition it should be clear, if you are using a text editor to write code you are making an API. Sense so much of the development community writing code works at this level, API in this form becomes useless.

We see articles talking about building APIs, they instruct how to build an API. What is happening? Well what they are asking is for you to consider the interface you're maintaining. Create stability in how your components talk to each other. It helps to isolate the work, if your micro service changes the rest API every release you have not decoupled implementation details with the integrated components. They would like to help you to define a good API.

Top comments (4)

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vikramchandra profile image
Vikram Sharma

This article on what is an api is also a great resource.

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jessekphillips profile image
Jesse Phillips

It is a good article, but not for knowing what an API is.

"Application Programming Interfaces (APIs) are ways for computer systems to β€˜talk’ to each other over internet protocols (HTTP, SMTP)"

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vikramchandra profile image
Vikram Sharma

Thanks for answering. My understanding is as under:
API is an interface to a program/framework/SDK etc. I am a Rails developer and the framework offers an API. Using this API my app can "talk" to the framework and perform tasks. APIs over internet protocols is a different category of APIs. REST Public API will fall in this category.

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vikramchandra profile image
Vikram Sharma

Agreed. The intro is a bit off. :)

DEV

Thank you.

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