[#CB3CEAF890DC04403F8545D792EC072443651A71]
Assignment
param& operator=(param_view const& other);
The members of `other` are copied, re-using already existing string capacity.
this->key == other.key && this->value == other.value && this->has_value == other.has_value
Linear in `other.key.size() + other.value.size()`.
Calls to allocate may throw.