[spatial.2] operator internal naming

[nmansard]

Change the name of operators. C++ operators are only trivial inline methods, while the code is in methods with an ad-hoc name. The name was yet taken from Python standards (for example plus for operator+, eq for operator==). They are now renamed following Eigen standards (add for operator+, isEqual for operator==).

[nmansard]

Whatever the choice, we should document the exhaustive list of internal operator naming for reference.

We need: Addition a+b Substraction a-b Multiplication a*b Equality test a==b In place addition a+=b In place substraction a-=b Allocation a=b Cross product a^b Dot product dot(a,b) Action a.se3action(b) Action inverse a.se3actionInv(b)

For future reference Python operators are here: https://docs.python.org/2/library/operator

For in-place operators, the internal operator typically should be implemented with an opposite structure (sorry this is not very clear), i.e. Template <D2> D& operator+= ( const D2 & d2 ) Would typically be implemented in D2 as D& D2::__peq__( D& d ) { ... return D; } This is the opposite convention used e.g in Python with __iadd__ which then makes Python convention directly suitable.

[nmansard]

We will use a mix: the same convention as in Eigen, but with XXX in prefix and suffix, and ending with impl when needed. For example: setTo __setTo__impl

Recall that there is possibly a problem with += (and other in-place operators). A+=B can be implemented as A.iadd(B) or as B.addTo(A). B.addTo(A) should be used first when possible. We may need to discuss the convention is A.iadd(B) is necessary.