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Creating native functions

Creating native functions — C functions as first-class JavaScript objects

Synopsis

#include <seed/seed.h>

SeedValue           (*SeedFunctionCallback)             (SeedContext ctx,
                                                         SeedObject function,
                                                         SeedObject this_object,
                                                         gsize argument_count,
                                                         const SeedValue arguments[],
                                                         SeedException *exception);
SeedObject          seed_make_function                  (SeedContext ctx,
                                                         SeedFunctionCallback func,
                                                         const gchar *name);
void                seed_create_function                (SeedContext ctx,
                                                         gchar *name,
                                                         SeedFunctionCallback func,
                                                         SeedObject obj);

Description

Exposing native C functions to JavaScript is one of the fundamental use cases for libseed when used in an embedding environment; if your application cannot be introspected, or you only have a small number of functions to expose, this is the simplest way to do that.

All native C callbacks should have the prototype of SeedFunctionCallback().

Example 10. Simple C program which embeds Seed with one exposed function

#include <glib.h>
#include <seed.h>
 
/* Our function, with the signature of SeedFunctionCallback(); say hello! */
SeedValue hello_world(SeedContext ctx,
                      SeedObject function,
                      SeedObject this_object,
                      gsize argument_count,
                      const SeedValue arguments[],
                      SeedException *exception)
{
    g_print("Hello, World!\n");
    return seed_make_null(ctx);
}
 
int main(gint argc, gchar ** argv)
{
    SeedEngine * eng;
 
    /* Initialize the Seed engine */
    eng = seed_init(&argc, &argv);
 
    /* Expose a C function to JavaScript */
    seed_create_function(eng->context, "hello_world",
                         (SeedFunctionCallback)hello_world,
                         eng->global);
 
    /* Call the newly created JavaScript function */
    seed_simple_evaluate(eng->context, "hello_world()", NULL);
 
    return 0;
}


Details

SeedFunctionCallback ()

SeedValue           (*SeedFunctionCallback)             (SeedContext ctx,
                                                         SeedObject function,
                                                         SeedObject this_object,
                                                         gsize argument_count,
                                                         const SeedValue arguments[],
                                                         SeedException *exception);

All native C function callbacks should use the prototype of SeedFunctionCallback.

ctx :

 A SeedContext

function :

 The SeedObject representing the function

this_object :

 The SeedObject representing the "this" object in the caller

argument_count :

 The number of arguments passed into the callback

arguments :

 An array of SeedValues; the value of the arguments passed in

exception :

 A reference to a SeedException; use seed_make_exception() in order to throw a JavaScript exception from the callback.

Returns :

 The SeedValue to return to the caller

seed_make_function ()

SeedObject          seed_make_function                  (SeedContext ctx,
                                                         SeedFunctionCallback func,
                                                         const gchar *name);

Creates a JavaScript object representing a first-class function; when the function is called from JavaScript, func will be called.

ctx :

 A valid SeedContext

func :

 A SeedFunctionCallback to implement the function.

name :

 The name of the function (used in exceptions).

Returns :

 A SeedObject representing the function

seed_create_function ()

void                seed_create_function                (SeedContext ctx,
                                                         gchar *name,
                                                         SeedFunctionCallback func,
                                                         SeedObject obj);

Creates a JavaScript object representing a first-class function; when the function is called from JavaScript, func will be called. Places the created function as the property name on obj.

ctx :

 A valid SeedContext

name :

 The name of the function (used in exceptions).

func :

 A SeedFunctionCallback to implement the function.

obj :

 The SeedObject on which to put the function.
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