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Avoiding Constructing Objects Using Proxy Objects

Explore how to optimize C++ code by avoiding the construction of temporary objects using proxy objects. Understand the implementation of a proxy class for string concatenation, enabling efficient comparisons without extra allocations. Learn about rvalue reference usage to prevent runtime errors and evaluate performance gains through benchmarking.

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Eager evaluation can have the undesirable effect that objects are unnecessarily constructed. Often this is not a problem, but if the objects are expensive to construct (because of heap allocations, for example), there might be legitimate reasons to optimize away the unnecessary construction of short-lived objects that serve no purpose.

Comparing concatenated strings using a proxy

We will now walk through a minimal example of using proxy objects to give you an idea of what they are and can be used for. It’s not meant to provide you with a general production-ready solution to optimizing string comparisons.

With that said, take a look at this code snippet that concatenates two strings and compares the result:

C++
auto a = std::string{"Cole"};
auto b = std::string{"Porter"};
auto c = std::string{"ColePorter"};
auto is_equal = (a + b) == c;
std::cout<<is_equal<<"\n";    //true

Here is a visual representation of the preceding code snippet:

Concatenating two strings into a new string
Concatenating two strings into a new string

The problem is that (a + b) constructs a new temporary string to compare it with c. Instead of constructing a new string, we can compare the concatenation right away, ...