Published August 10, 2018 There is a particular case for default parameters: it’s when their type is a template type. Even though the idea is similar to the regular default parameters, there are some subtleties that are worth mentioning. To illustrate this, I will use the example of, the output iterator for aggregating data into a map, for which we have a new requirement: default aggregation. What makes this case interesting is that. it’s harder to get right than simple default parameters,. it shows a practical illustration of the dilemna between overloads and default parameters. This post is part of a series on default parameters:.
![Template Template](/uploads/1/2/5/4/125426810/652913424.png)
Default Parameters With Default Template Type Parameters.: a helper to work around default parameters constraints. Application to mapaggregator is a component that helps aggregating new data into a map in a very concise manner. It is an output iterator, much like std::backinserter, that you can plug onto a map and that will:.
either insert new data if its key isn’t already in the map,. or aggregate the new value with the one in the map correponding to this key. Mapaggregator takes an aggregating function, like concatenateStrings, to know how to aggregate a new value with an existing one. Here is a usage example.
(And we saw there how we could achieve the same purpose by using overloads.) Default parameters, a better alternative? This is the part where I had to fumble around the most to get it right. To use a default parameter whose type is a template, you need to set this template parameter as optional too. Indeed, if you set it as a regular template parameter and call the function without specifying a value, the compiler can’t deduce the type for the template.
The business process template parameters form includes the following tabs: General, Parameters, Variables and Access. The General tab, among the fields common for most of the objects (Name and Description) includes the options controlling the way the process is started.
Unless the template is deducible another way (with another argument, or specified explicitly at call site) in which case you don’t need a default type for the template. So this is what it looks like for mapaggregator.