fullmatch and
pairmatch create optimal matchings of
treated and control units given a matrix (or similar
representation) of distances between treated and control
units. These distance specifications must implement
certain generic functions. This function checks that all
necessary methods exist and the object can be used to
specify distances in a way that the matching functions
can use.validDistanceSpecification(distance,
stopOnProblem = TRUE)TRUE (default) the
function will raise an error for invalid objects.
Otherwise, it returns a logical.