CODESAMPLE

Template Method - C

Template Method C

The Template Method pattern defines the skeleton of an algorithm in a base class, deferring some steps to subclasses. It lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure. In this C implementation, AbstractOperation is the abstract base class defining the overall operation with execute() as the template method. Concrete operation classes (ConcreteOperationA, ConcreteOperationB) implement the abstract performOperation() to provide specific behavior. This avoids code duplication while maintaining a consistent workflow across different operations. C’s function pointers facilitate this pattern, allowing the base class to call the subclass’s implementation.

#include <stdio.h>

// Abstract Class
typedef struct AbstractOperation {
    void (*performOperation)(struct AbstractOperation* self); // Function pointer
    void (*step1)(struct AbstractOperation* self);
    void (*step2)(struct AbstractOperation* self);
} AbstractOperation;

void abstract_operation_step1(AbstractOperation* self) {
    printf("AbstractOperation: Step 1\n");
}

void abstract_operation_step2(AbstractOperation* self) {
    printf("AbstractOperation: Step 2\n");
}

void abstract_operation_execute(AbstractOperation* self) {
    self->step1(self);
    self->performOperation(self);
    self->step2(self);
}

// Concrete Class A
typedef struct ConcreteOperationA : AbstractOperation {
    void (*performOperation)(struct AbstractOperation* self);
};

void concrete_operation_a_performOperation(AbstractOperation* self) {
    printf("ConcreteOperationA: Performing operation A\n");
}

void concrete_operation_a_init(struct ConcreteOperationA* op) {
    op->performOperation = concrete_operation_a_performOperation;
}

// Concrete Class B
typedef struct ConcreteOperationB : AbstractOperation {
    void (*performOperation)(struct AbstractOperation* self);
};

void concrete_operation_b_performOperation(AbstractOperation* self) {
    printf("ConcreteOperationB: Performing operation B\n");
}

void concrete_operation_b_init(struct ConcreteOperationB* op) {
    op->performOperation = concrete_operation_b_performOperation;
}


int main() {
    struct ConcreteOperationA opA;
    opA.step1 = abstract_operation_step1;
    opA.step2 = abstract_operation_step2;
    concrete_operation_a_init(&opA);

    printf("Executing Concrete Operation A:\n");
    abstract_operation_execute(&opA);
    printf("\n");

    struct ConcreteOperationB opB;
    opB.step1 = abstract_operation_step1;
    opB.step2 = abstract_operation_step2;
    concrete_operation_b_init(&opB);

    printf("Executing Concrete Operation B:\n");
    abstract_operation_execute(&opB);

    return 0;
}