Getting started¶

Welcome to D:YAML! D:YAML is a YAML parser library for the D programming language. This tutorial will explain how to set D:YAML up and use it in your projects.

This is meant to be the simplest possible introduction to D:YAML. Some of this information might already be known to you. Only basic usage is covered.

Setting up¶

Install the DMD compiler¶

Digital Mars D compiler, or DMD, is the most commonly used D compiler. You can find its newest version here. Download the version of DMD for your operating system and install it.

Note

Other D compilers exist, such as GDC and LDC.

Download and compile D:YAML¶

The newest version of D:YAML can be found here. Download a source archive, extract it, and move to the extracted directory.

D:YAML uses a modified version of the CDC script for compilation. To compile D:YAML, you first need to build CDC. Do this by typing the following command into the console:

dmd cdc.d

Now compile D:YAML with CDC. To do this on Unix/Linux, use the following command:

./cdc

On Windows:

cdc.exe

This will compile the library to a file called libdyaml.a on Unix/Linux or libdyaml.lib on Windows.

Your first D:YAML project¶

Create a directory for your project and in that directory, create a file called input.yaml with the following contents:

Hello World :
    - Hello
    - World
Answer: 42

This will serve as input for our example.

Now we need to parse it. Create a file called main.d. Paste following code into the file:

import std.stdio;
import yaml;

void main()
{
    //Read the input.
    Node root = Loader("input.yaml").load();

    //Display the data read.
    foreach(string word; root["Hello World"])
    {
        writeln(word);
    }
    writeln("The answer is ", root["Answer"].as!int);

    //Dump the loaded document to output.yaml.
    Dumper("output.yaml").dump(root);
}

Explanation of the code¶

First, we import the yaml module. This is the only D:YAML module you need to import - it automatically imports all needed modules.

Next we load the file using the Loader.load() method. Loader is a struct used for parsing YAML documents. The load() method loads the file as one YAML document, or throws YAMLException, D:YAML exception type, if the file could not be parsed or does not contain exactly one document. Note that we don’t do any error checking here in order to keep the example as simple as possible.

Node represents a node in a YAML document. It can be a sequence (array), mapping (associative array) or a scalar (value). Here the root node is a mapping, and we use the index operator to get subnodes with keys “Hello World” and “Answer”. We iterate over the first, as it is a sequence, and use the Node.as() method on the second to read its value as an integer.

You can iterate over a mapping or sequence as if it was an associative or normal array. If you try to iterate over a scalar, it will throw a YAMLException.

You can iterate over subnodes using Node as the iterated type, or specify the type subnodes are expected to have. D:YAML will automatically convert iterated subnodes to that type if possible. Here we specify the string type, so we iterate over the “Hello World” sequence as an array of strings. If it is not possible to convert to iterated type, a YAMLException is thrown. For instance, if we specified int here, we would get an error, as “Hello” cannot be converted to an integer.

The Node.as() method is used to read value of a scalar node as specified type. D:YAML will try to return the scalar as this type, converting if needed, throwing YAMLException if not possible.

Finally we dump the document we just read to output.yaml with the Dumper.dump() method. Dumper is a struct used to dump YAML documents. The dump() method writes one or more documents to a file, throwing YAMLException if the file could not be written to.

D:YAML doesn’t preserve style information in documents, so even though output.yaml will contain the same data as input.yaml, it might be formatted differently. Comments are not preserved, either.

Compiling¶

To compile your project, DMD needs to know which directories contain the imported modules and the library. You also need to tell it to link with D:YAML. The import directory should be the source subdirectory of the D:YAML directory. You can specify it using the -I option of DMD. The library directory should point to the compiled library. On Unix/Linux you can specify it using the -L-L option, and link with D:YAML using the -L-l option. On Windows, the import directory is used as the library directory. To link with the library on Windows, just add the path to it relative to the current directory.

For example, if you extracted and compiled D:YAML in /home/xxx/dyaml, your project is in /home/xxx/dyaml-project, and you are currently in that directory, compile the project with the following command on Unix/Linux:

dmd -I../dyaml/source -L-L../dyaml -L-ldyaml main.d

And the following on Windows:

dmd -I../dyaml/source ../dyaml/libdyaml.lib main.d

This will produce an executable called main or main.exe in your directory. When you run it, it should produce the following output:

Hello
World
The answer is 42

Conclusion¶

You should now have a basic idea about how to use D:YAML. To learn more, look at the API documentation and other tutorials. You can find code for this example in the example/getting_started directory in the package.

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