This put overload fixes a very major bug.

[hrissan]

Consider dbi.put(txn, key, val{data, size});
as val is not an lvalue, the following template overload will be selected.
template<typename K, typename V>
bool put(MDB_txn* const txn,
const K& key,
const V& val,
const unsigned int flags = default_put_flags) {
const lmdb::val k{&key, sizeof(K)};
lmdb::val v{&val, sizeof(V)};
return lmdb::dbi_put(txn, handle(), k, v, flags);
}
Which instead of storing (data, size) will store (&val, sizeof(val))

[hoytech]

I agree that these templated methods were a bad idea. I have removed them in my lmdbxx fork, and documented some alternatives in the README.