# Templates

You have hopefully already noticed that certain classes in the C++
standard library are «parametric»: they can be «instantiated» with
different «type parameters»: that is, we can create an ‹std::vector›
of integers, but we can also create an ‹std::vector› of
floating-point numbers. Even more interestingly, we can create an
‹std::vector› of instances of our own classes. It is probably quite
clear that there is a single entity called ‹std::vector›: this
entity is called a «class template». Unfortunately, the terminology
gets slightly confusing here: the «instances» of «class templates»
are «classes».  This is different from «objects» which are also
known as «class instances».

Demonstrations:

 1. ‹zipper›   – our favourite data structure, now generic
 2. ‹expr›     – a different take on expressions
 3. ‹fold›     – function templates
 4. ‹rel›      – non-type template arguments

Elementary exercises:

 1. ‹iota›     – generate an integer sequence
 2. ‹quot›     – quotient fields (aka fields of fractions)
 3. ‹split›    – slice a string view into two on a delimiter

Free exercises:

 1. ‹tfold›    – fold a tree using an arbitrary function
 2. ‹tmap›     – apply a function to each node
 3. ‹monoid›   – free monoids and homomorphisms

Graded exercises:

 1. ‹circular› – a circular list, but generic
 2. ‹buffer›   – a fixed-size queue-like data structure
 3. ‹stats›    – median, quartiles, mode over any container
 4. ‹sparse›   – sparse copy-on-write arrays
 5. ‹bbox›     – a bounding box of a point collection
 6. ‹visit›    – call a function on each node of a graph