C Inheritance: Decorator Pattern

Readme.md

Decorator Pattern in C

• Basic C Inheritance
• No Destructor implemented

decorator.c

#include <stdlib.h>
#include <stdio.h>
#include <Kernel/string.h>
#include "decorator.h"

/** Constructors **/

Writer_t* create_writer() {
    Writer_t* writer = (Writer_t*) malloc(sizeof(StarWriter_t));
    if (writer == 0) return 0;

    writer->base.print = writer_print;
    writer->base.type.type = "Writer";

    return writer;
}

EndlineWriter_t* create_endline_writer(WriterComponent_t* component) {
    EndlineWriter_t* writer = (EndlineWriter_t*) malloc(sizeof(EndlineWriter_t));
    if (writer == 0) return 0;

    writer->base.base.print = endline_writer_print;
    writer->base.base.type.type = "EndlineWriter";
    writer->base.component = component;

    return writer;
}

StarWriter_t* create_star_writer(WriterComponent_t* component) {
    StarWriter_t* writer = (StarWriter_t*) malloc(sizeof(StarWriter_t));
    if (writer == 0) return 0;

    writer->base.base.print = star_writer_print;
    writer->base.base.type.type = "StarWriter";
    writer->base.component = component;

    return writer;
}

/** Class Methods **/

int instance_of(WriterComponent_t* this, const char* instance) {
    return (strcmp(this->type.type, instance));
}


/** Print Methods **/

char* writer_print(void* this, char* data, size_t max_size) {
    printf(data);
    return data;
};

char* endline_writer_print(void* this, char* data, size_t max_size) {
    EndlineWriter_t* obj = (EndlineWriter_t*) this;
    // Add \n to data
    size_t length = strlen(data);
    if (length < max_size - 1) {
        data[length] = '\n';
        data[length + 1] = '\0';
    }

    return obj->base.component->print(obj->base.component, data, max_size);
}

char* star_writer_print(void* this, char* data, size_t max_size) {
    StarWriter_t* obj = (StarWriter_t*) this;
    // Add * to data
    size_t length = strlen(data);
    if (length < max_size - 1) {
        data[length] = '*';
        data[length + 1] = '\0';
    }

    return obj->base.component->print(obj->base.component, data, max_size);
}

decorator.h

#ifndef _H_DECORATOR
#define _H_DECORATOR

#include <stdio.h>

/**
* Used to ask what type the object is:
* The string is the classname
*/
typedef struct Type {
    char* type;
} Type_t;

/**
* Abstract Writer Component
*/
typedef struct WriterComponent {
    Type_t type;

    char* (* print)(void* this, char* data, size_t max_length);
} WriterComponent_t;

/**
* Abstract Writer Decorator
*/
typedef struct WriterDecorator {
    WriterComponent_t base;
    WriterComponent_t* component;
} WriterDecorator_t;

int instance_of(WriterComponent_t* this, const char* class);


/**
* Concrete Component: Writer
*/
typedef struct Writer {
    WriterComponent_t base;
} Writer_t;

Writer_t* create_writer();

char* writer_print(void* this, char*, size_t);

/**
* Concrete Decorator: EndlineWriter
* Attach a new line at the end of the string
*/
typedef struct EndlineWriter {
    WriterDecorator_t base;
} EndlineWriter_t;

EndlineWriter_t* create_endline_writer(WriterComponent_t* component);

char* endline_writer_print(void* this, char*, size_t);

/**
* Concrete Decorator: Star Writer
* Attach a * at the end of the string
*/
typedef struct StarWriter {
    WriterDecorator_t base;
} StarWriter_t;

StarWriter_t* create_star_writer(WriterComponent_t* component);

char* star_writer_print(void* this, char*, size_t);

#endif

main.c

#include "decorator.h"

int main() {
    char text[20] = {'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd', '\0'};
    WriterComponent_t* writer = (WriterComponent_t*) create_star_writer((WriterComponent_t*) create_endline_writer((WriterComponent_t*) create_writer()));
    writer->print(writer, text, 20);

    printf(writer->type.type); // Will print StarWriter
    return 0;
}