[test][distance] add missing typename
[distance] remove inner template parameter that shadows global
template parameter; qualify template method call with template keyword;
fix return type of variant visitors;
[test][assign] fix errors in test of variant support for assign
Merge pull request #41 from mkaravel/feature/distance

Feature/distance fix errors in variant support
Merge pull request #42 from mkaravel/feature/assign

[test][assign] fix errors in test of variant support for assign