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package org.luaj.vm2.lib;
import org.luaj.vm2.LuaError;
import org.luaj.vm2.LuaFunction;
import org.luaj.vm2.LuaValue;
/**
* Subclass of {@link LuaFunction} common to Java functions exposed to lua.
* <p>
* To provide for common implementations in JME and JSE,
* library functions are typically grouped on one or more library classes
* and an opcode per library function is defined and used to key the switch
* to the correct function within the library.
* <p>
* Since lua functions can be called with too few or too many arguments,
* and there are overloaded {@link LuaValue#call()} functions with varying
* number of arguments, a Java function exposed in lua needs to handle the
* argument fixup when a function is called with a number of arguments
* differs from that expected.
* <p>
* To simplify the creation of library functions,
* there are 5 direct subclasses to handle common cases based on number of
* argument values and number of return return values.
* <ul>
* <li>{@link ZeroArgFunction}</li>
* <li>{@link OneArgFunction}</li>
* <li>{@link TwoArgFunction}</li>
* <li>{@link ThreeArgFunction}</li>
* <li>{@link VarArgFunction}</li>
* </ul>
* <p>
* To be a Java library that can be loaded via {@code require}, it should have
* a public constructor that returns a {@link LuaValue} that, when executed,
* initializes the library.
* <p>
* For example, the following code will implement a library called "hyperbolic"
* with two functions, "sinh", and "cosh":
* <pre> {@code
* import org.luaj.vm2.LuaValue;
* public class hyperbolic extends org.luaj.vm2.lib.OneArgFunction {
* public hyperbolic() {}
* public LuaValue call(LuaValue arg) {
* switch ( opcode ) {
* case 0: {
* LuaValue t = tableOf();
* this.bind(t, hyperbolic.class, new String[] { "sinh", "cosh" }, 1 );
* env.set("hyperbolic", t);
* return t;
* }
* case 1: return valueOf(Math.sinh(arg.todouble()));
* case 2: return valueOf(Math.cosh(arg.todouble()));
* default: return error("bad opcode: "+opcode);
* }
* }
* }
* }</pre>
* The default constructor is both to instantiate the library
* in response to {@code require 'hyperbolic'} statement,
* provided it is on Javas class path,
* and to instantiate copies of the {@code hyperbolic}
* class when initializing library instances. .
* The instance returned by the default constructor will be invoked
* as part of library loading.
* In response, it creates two more instances, one for each library function,
* in the body of the {@code switch} statement {@code case 0}
* via the {@link #bind(LuaValue, Class, String[], int)} utility method.
* It also registers the table in the globals via the {@link #env}
* local variable, which should be the global environment unless
* it has been changed.
* {@code case 1} and {@code case 2} will be called when {@code hyperbolic.sinh}
* {@code hyperbolic.sinh} and {@code hyperbolic.cosh} are invoked.
* <p>
* To test it, a script such as this can be used:
* <pre> {@code
* local t = require('hyperbolic')
* print( 't', t )
* print( 'hyperbolic', hyperbolic )
* for k,v in pairs(t) do
* print( 'k,v', k,v )
* end
* print( 'sinh(.5)', hyperbolic.sinh(.5) )
* print( 'cosh(.5)', hyperbolic.cosh(.5) )
* }</pre>
* <p>
* It should produce something like:
* <pre> {@code
* t table: 3dbbd23f
* hyperbolic table: 3dbbd23f
* k,v cosh cosh
* k,v sinh sinh
* sinh(.5) 0.5210953
* cosh(.5) 1.127626
* }</pre>
* <p>
* See the source code in any of the library functions
* such as {@link BaseLib} or {@link TableLib} for specific examples.
*/
abstract public class LibFunction extends LuaFunction {
/** User-defined opcode to differentiate between instances of the library function class.
* <p>
* Subclass will typicall switch on this value to provide the specific behavior for each function.
*/
protected int opcode;
/** The common name for this function, useful for debugging.
* <p>
* Binding functions initialize this to the name to which it is bound.
*/
protected String name;
/** Default constructor for use by subclasses */
protected LibFunction() {
}
public String tojstring() {
return name != null? name: super.tojstring();
}
/**
* Bind a set of library functions.
* <p>
* An array of names is provided, and the first name is bound
* with opcode = 0, second with 1, etc.
* @param env The environment to apply to each bound function
* @param factory the Class to instantiate for each bound function
* @param names array of String names, one for each function.
* @see #bind(LuaValue, Class, String[], int)
*/
protected void bind(LuaValue env, Class factory, String[] names ) {
bind( env, factory, names, 0 );
}
/**
* Bind a set of library functions, with an offset
* <p>
* An array of names is provided, and the first name is bound
* with opcode = {@code firstopcode}, second with {@code firstopcode+1}, etc.
* @param env The environment to apply to each bound function
* @param factory the Class to instantiate for each bound function
* @param names array of String names, one for each function.
* @param firstopcode the first opcode to use
* @see #bind(LuaValue, Class, String[])
*/
protected void bind(LuaValue env, Class factory, String[] names, int firstopcode ) {
try {
for ( int i=0, n=names.length; i<n; i++ ) {
LibFunction f = (LibFunction) factory.newInstance();
f.opcode = firstopcode + i;
f.name = names[i];
f.env = env;
env.set(f.name, f);
}
} catch ( Exception e ) {
throw new LuaError( "bind failed: "+e );
}
}
/** Java code generation utility to allocate storage for upvalue, leave it empty */
protected static LuaValue[] newupe() {
return new LuaValue[1];
}
/** Java code generation utility to allocate storage for upvalue, initialize with nil */
protected static LuaValue[] newupn() {
return new LuaValue[] { NIL };
}
/** Java code generation utility to allocate storage for upvalue, initialize with value */
protected static LuaValue[] newupl(LuaValue v) {
return new LuaValue[] { v };
}
}