Re: Debug help - foreach opApply overload School example: Programming in D

[Brother Bill via Digitalmars-d-learn]

On Monday, 18 August 2025 at 17:58:54 UTC, Dejan Lekic wrote:
So, to fix your error, you can remove the "const" method 
qualifier from opApply, or cast the const away from the member 
when you use it.

Thanks for the tip.  It just needed more 'const' keywords 
sprinkled in here and there.

Here is a working example:
```
STUDENTS
Bob
Carol
Ted
Alice

TEACHERS
Mr. Smith
Dr. Kildare
Albert Einstein
```

source/app.d
```
import std.stdio;

void main() {
        auto school = new School;

        school.addStudent("Bob");
        school.addStudent("Carol");
        school.addStudent("Ted");
        school.addStudent("Alice");

        school.addTeacher("Mr. Smith");
        school.addTeacher("Dr. Kildare");
        school.addTeacher("Albert Einstein");

        writeln("STUDENTS");
        foreach (const Student student; school) {
                writeln(student.name);
        }
        writeln;

        writeln("TEACHERS");
        foreach (const Teacher teacher; school) {
                writeln(teacher.name);
        }
}

class School {
        Student[] students;
        Teacher[] teachers;

        int opApply(int delegate(ref const Student) dg) const {
                int result = 0;

                for (int i = 0; i < students.length; ++i) {
                        const Student student = students[i];
                        result = dg(student);
                        if (result)
                                break;
                }

                return result;
        }

        int opApply(int delegate(const ref Teacher) dg) const {
                int result = 0;

                for (int i = 0; i < teachers.length; ++i) {
                        const Teacher teacher = teachers[i];
                        result = dg(teacher);
                        if (result)
                                break;
                }
                return result;
        }

        void addStudent(string studentName) {
                students ~= new Student(studentName);
        }

        void addTeacher(string teacherName) {
                teachers ~= new Teacher(teacherName);
        }
}

class Student {
        string name;

        this(string name) {
                this.name = name;
        }
}

class Teacher {
        string name;

        this(string name) {
                this.name = name;
        }
}

```