MQL4 Documentation: Modifier '&' and Keyword 'this'

Passing Parameters by Reference

**Simple Types:** Can be passed by value or by reference.

**Compound Types (Arrays, Structures, Class Objects):** Always passed by reference.

**Reference Modifier (&):** Added before the parameter name in the function header to indicate passing by reference. Changes to the parameter inside the function affect the original variable.

**Preventing Modification:** Use the const modifier with & (e.g., const double &array[]) to prevent changes to parameters passed by reference.

**Arrays and Structures:** The & symbol is obligatory when passing arrays and structures as function parameters.

**Array Assignment:** Direct assignment of one array to another is not allowed; element-wise copying is required.

**Example:**

class CDemoClass {
private:
  double m_array[];
public:
  void setArray(double &array[]);
};
void CDemoClass::setArray(double &array[]) {
  if(ArraySize(array) > 0) {
    ArrayResize(m_array, ArraySize(array));
    ArrayCopy(m_array, array);
  }
}

Keyword this

**Purpose:** Provides a reference to the current object within its class or structure methods.

**Usage:** this always refers to the object whose method is being executed.

**Getting Object Pointer:** GetPointer(this) returns a pointer to the current object.

**Returning Object Pointers:** Functions can return object pointers using GetPointer(this) (e.g., CDemoClass *getDemoClass() { return(GetPointer(this)); }).

**Limitations:**

* Structures do not have pointers. * Operators new and delete cannot be applied to structures. * GetPointer(this) cannot be used within structure methods.

**Example:**

class CDemoClass {
private:
  double m_array[];
public:
  void setArray(double &array[]);
  CDemoClass *getDemoClass();
};
CDemoClass *CDemoClass::getDemoClass(void) {
  return(GetPointer(this));
}

Related Topics

[Object Pointers](/basis/types/object_pointers)

[Creating and Deleting Objects](/basis/variables/object_live)

[Visibility Scope and Lifetime of Variables](/basis/variables/variable_scope)