A very simple example of static website using golang, martini and markdown.
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- In this tutorial we look at how you can add images to your hugo content pages.
- Yup there is a markdown parser. The problem is I am hosting the markdown and images for display from a golang web server. The server needs to know the location of the images. When the author of the markdown puts a relative path, I need to change that to an absolute path.
An interface is something I first stumbled upon when I started learning compiled languages. I had read the term a couple of times before, but really only with C, Java and lately Go an interface actually means something to me that I can remember.
I’ve used the abbreviation API about one thousand times in my life, which stands for Application programming interface, usually I mean web APIs, where I get some JSON to feed it to my frontend or something, but that’s already a very specific use case.
As with many words in computer science, interface can mean many things, but depending on context it means a very specific thing. To quote wikipedia:
In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information.
and more specifically regarding programming:
the term interface is used to define an abstract type that contains no data but defines behaviours as method signatures.
So an interface is a bit like a puzzle piece. You can’t just attach your code or your function anywhere, but you need to find the right part that’s sticking out.
Implementing / Satisfying Intefaces
To implement or to satisfy an interface means to comply with the rules set by the blueprint. In object oriented languages such as C# or Java, interfaces are abstract classes, that just set some requirements for which functions must be included and which types they can receive or return.
Since Golang is not an object oriented language, there are no classes to implement, but we can still satisfy an interface with our type and it will be checked automatically by the compiler. Let’s pretend we are programming a series of vending machines and instead of a <Product> type, they’re supposed to return a string:
Golang Markdown Renderer
You can see that type VendingMachine interface creates the first blueprint interface and the Cola struct now will need to satisfy the interface by also having a ReturnItem function.
We test this by creating a variable vend1 of type VendingMachine and assign a Cola{} struct to it.
The expected output is: you get a cooled cola
If we remove the following code:
We get the error:
Thanks Go! Helpful! This way we can’t forget the essential ReturnItem function in our VendingMachine and make our customers really angry at us, because no products come out after they payed.
Similarly, if we change the return type of the Cola ReturnItem to int:
This makes sure that we return the correct type as well, because the humans or possibly robots interfacing with our vending machine will expect strings, not integers to come out.
Lastly, when coming from other languages you might try to implement a go interface by using the interface to create a type instance, maybe like this:
Golang Markdown Parser
However, since the implements checking is done by the compiler and abstracted away, you’ll only get an error about a composite literal:
Golang Markdown Blog
Summary
Interfaces are handy tools to ensure that your application can have consistently grouped functionalities with different values, even in a non OOP language like Go.
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Golang Markdown Generator
Real world examples of interfaces are the Readers and Writers in Go are IO parts like the Writer or Reader which you can try out and extend for some simple file system operations if you’re interested.