ECE39595-Homework 8 Solved

Description

You should convert the supplied program into three forms:

1. A program that only uses unique_ptr
2. A program that only uses shared_ptr and does initialization using std::shared_ptr<Type1>(new Type2(args))

where Type2 ISA Type1

3. A program that only uses shared_ptr and does initialization using std::make_shared<Type1>(Type2(…))

where Type1 is not abstract and Type2 ISA Type1. More on why Type1 should not be abstract below under “Some useful information”.

Some useful information.

First bit of useful information:

When you have a statement that looks like an assignment but is doing an initialization, e.g.,

Type1 var = std::move(unique_ptr<Type1>(new Type2(args)));

or

var = std::move(unique_ptr<Type1>(new Type2(args)));

or

Type1( ) : var(std::move(unique_ptr<Type1>(new Type2(args)))) {. . .}

where var is an object field and the statement is an initialization being performed in a constructor, C++ is actually doing an initialization and not an assignment. In these cases you do not have to use std::move(…), and the statements above could be correctly written as: Type1 var = unique_ptr<Type2>(new Type2(args)); var = unique_ptr<Type2>(new Type2(args));

Type1( ) : var(unique_ptr<Type1>(new Type2(args))) {. . .}

However, if you use std::move it will not be an error.

Second bit of useful information:

C++ tries to make the semantics of shared_ptr match the semantics of raw C pointers as closely as possible. It also tries to make the semantics of make_shared mimic the semantics of new as much as possible. As a result, if you code:

std::shared<AbstractBase> sp = std::make_shared<AbstractBase>(DerivedNotAbstract( ));

this mimicking new you will cause you to get an error since std::make_shared<AbstractBase> will be treated as an attempt to create a new AbstractBase object. The correct way to do this is to do:

std::shared<AbstractBase> sp = std::make_shared<DerivedNotAbstract>(DerivedNotAbstract());

For those of you that remember last semester when I talked about the desire to program to interfaces, the use of the concrete DerivedNotAbstract twice should be bothersome. This can be avoided by having a factory method, std::shared_ptr<AbstractBase> factory(…) {…}  and use it to do the initialization, e.g.,

std::shared<AbstractBase> sp = factory(“Derived”); but this is not necessary for this homework.