Avoiding Lengthy C++ Template Instantiations
C++ templates are a powerful mechanism that can be used to create generic code. With templates, it is also possible to remove undesirable code duplication, since the same code can then be applied to data of different types.
On the flip-side, however, templates can also create problems due to the potential they have to slow down compilation times. Because all the code in a template is generally available to the compiler when processing translation units, it is difficult to provide separate compilation for templates. An example of library that is victim of this behavior is boost, where typically all the functionality is included in header files. These header files are then included each time the library is referenced in an implementation file, resulting in long build times.
Despite these shortcomings, in some situations it is possible to reduce the amount of work done by the compiler in behalf of templates. This article shows a simple technique that can be used to achieve faster template compilation speeds in the particular case in which desired instantiations are known ahead of time.
Pre-Instantiating Templates
Certain templates are known to be used in only a reduced number of cases. For example, consider a numeric library that creates code for different floating point types. Each class in the library can be instantiated with a particular floating point type, such as double, long double, or float. Consider for instance the following definition:
// file mathop.h
template <class T>
class MathOperations {
public:
static T squared(T value) {
return value * value;
}
// ... };
This class can be used in the following way:
#include <mathop.h>
MathOperations<double> mathOps; double value = 2.5;
cout << "result: " << mathOps.squared(2.5) << endl;
Unfortunately, because the class MathOperations is a template class, we have to include its complete definition as part of the header file, where it can be found by the compiler whenever the class is instantiated.
A possible way to reduce the size of the header file is to pre-instantiate the template for the types that we known in advance.
The first step is to remove the implementation from the header file. This is clearly possible, since you can implement class member functions outside the class declaration (if the class is a template or not). Then, you need to add the implementation to a separate source file. Once this step is done, client code will be able to use the template class interface, but will not be able to generate code. Therefore, for this to work, you need to instantiate the templates on the implementation file.
// file mathop.h
template <class T>
class MathOperations {
public:
static T squared(T value);
// ...
};
// file mathop.cpp
// template member function definition
template <class T>
T MathOperations<T>::squared(T value) {
return value * value;
}
void instantiateMathOps() {
double d = MathOperations<double>::squared(2.0);
float f = MathOperations<float>::squared(2.0);
int i = MathOperations<int>::squared(2);
long l = MathOperations<long>::squared(2);
char c = MathOperations<char>::squared(2);
}
In the example above, I chose to instantiate five versions of the original template for numeric types. The main limitation of this technique, as I mentioned above, is that your clients will not be able to generate templates for the additional types they may want to use. However, in a few situations you may really want to restrict how these templates are used, and the technique above works as desired.
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About the Author
Carlos Oliveira holds a PhD in Systems Engineering and Optimization from University of Florida. He works as a software engineer, with more than 10 years of experience in developing high performance, commercial and scientific applications in C++, Java, and Objective-C. His most Recent Book is Practical C++ Financial Programming.
Causes Real Estate Companies Want to a Certified Roofing Expert in Wilmington
Properties by the ocean, like Wilmington, face unique challenges regarding roof upkeep. Employing a qualified roofing company is essential for addressing these challenges and ensuring the durability of coverings.
Highlighted are some reasons why property owners should seriously consider engaging qualified roofing assistance in Wilmington, North Carolina:
Motivations Homeowners Would Hire a Certified Roofing Expert in Coastal NC
Properties in coastal areas, like Wilmington, deal with distinct problems regarding roof upkeep. Employing a certified roofing expert is vital for managing these issues and guaranteeing the lifespan of roofing systems.
Here are some reasons why homeowners ought to think about employing professional roofing services in Wilmington:
Hurricane Repair
Coastal areas frequently face extreme conditions like hurricanes, resulting in extensive harm to roofing systems. A qualified company can accurately assess and repair storm damage to avert subsequent damage.
Salt Atmosphere Corrosion Avoidance
Salty air might result in rust of roofing materials, particularly steel roofs. Frequent checks by a qualified individual can detect initial indicators of rust and utilize protective treatments to enhance the lifespan of the roof.
Dampness Control plus Drip Fix
Coastal regions are subject to damp conditions, which may cause dampness under roofing materials, causing leaks and water damage. A certified expert can handle moisture problems effectively and perform necessary repairs to prevent subsequent issues.
Sufficient Airflow Installation
Sufficient covering ventilation is crucial for avoiding dampness accumulation and ensuring the condition of covering substances. A licensed roofer can install airflow solutions that suit the specific needs of coastal homes.
Substance Knowledge and Suggestions
Qualified companies hold comprehensive awareness of the best materials for oceanfront climates. They can recommend materials that can endure corrosion, dampness, and wind damage, guaranteeing extended durability for roofs.
Understanding these factors is crucial as it can lower expenses in the long run. Proactive maintenance and prompt fixes can prevent costly damage and enhance the lifespan of the roofing, ensuring the protection of the residence in seaside regions.
Seaside regions are prone to temperature including storms, leading to substantive destruction to roofing systems. A expert company can precisely evaluate and fix violent storm damage to avert ensuing damage.
Ocean Atmosphere Oxidation Prevention
Saline atmosphere can cause rust of covering substances, especially metal roofs. Regular inspections by a professional can identify early signs of rust and make the most of precautionary measures to enhance the longevity of the roof.
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Coastal regions experience high humidity, which might result in moisture content buildup under roofing products, leading to seepages and also structural harm. A expert company can manage moisture content effectively to necessary repairs to prevent additional harm.
Sufficient Ventilation Setup
Sufficient protecting air flow is vital for avoiding dampness buildup and keeping the quality of protecting materials. A accredited roofer can set up air-flow that suit the distinct conditions of beachfront investment properties.
Substance Expertise plus Suggestions
Qualified companies hold detailed awareness of the best materials for oceanfront climates. They’ll suggest materials that can withstand corrosion, humidity, and storm effects, guaranteeing extended durability for coverings.
staying informed of these details is important since it is able to cut down on costs eventually. Pro-active service and immediate restorations can avoid expensive harm and prolong the life of the roof, ensuring the security of the house in resort regions.
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