Kotlin Domain specific language （DSL）

DSL What is it?

For me DSL Is a familiar and unfamiliar word , I always feel that I often see it, but I don't know what it is . For ease of understanding, it is necessary to mention programing language , We are all familiar with this , such as Java、kotlin All belong to programing language , and DSL Its full name is “ Domain specific language ”. The following is a comparison of the two ：

• programing language ： There is a set of sufficient and perfect abilities to solve almost all problems that can be solved by computers .
• DSL： Focus on specific tasks , Or in the field , And give up functions irrelevant to this field .

It can be seen that , A language that is specific to the existence of a special function and can only complete this part of the function is called Domain specific language . Common are DSL Yes SQL And regular expressions .

Embedded DSL

Embedded DSL As kotlin A new feature of , It can facilitate our development . Then why use inline DSL Instead of using it directly , With SQL For example .

These languages in order to achieve their goals more effectively , Passing will reduce the functions they provide , So when you need to execute a SQL At the time of statement , Don't declare a class or method , every last keyword It represents the operation and type to be performed , Each type of operation has its own unique Of grammar And keyword sets for specific tasks .

And often DSL Language tends to be declarative , And general programming language contrary , Mostly orders .

This leads to direct use DSL There is a drawback ： They are difficult to interact with host applications that use a common programming language combination Get up and use . Simply put, the grammar is different , It needs to be passed in string and other forms , Inconvenient Correct mistakes in time .

Example

Anko SQLite（SQL）

fun getUsers(db: ManagedSQLiteOpenHelper): List<User> = db.use {
    db.select("Users")
            .whereSimple("family_name = ?", "John")
            .doExec()
            .parseList(UserParser)
}

Anko Layouts（XML）

verticalLayout {
    val name = editText()
    button("Say Hello") {
        onClick { toast("Hello, ${name.text}!") }
    }
}

summary

kotlin Embedded with DSL It makes the writing of some special domain languages easier and more unified . When proficient, you can even stop writing XML File layout , No more hard to remember and inconvenient to debug SQL sentence .（ Although I am still used to using XML Write layout ）

The principle of its implementation is also very simple , In fact, the common method is based on lambda The form of expression completes the highly concise code style . To put it bluntly, it is to complete the above functions in the form of code , But these codes have been kotlin Deeply encapsulated and optimized .