Those who beat their chest and proclaim "I'm a Constitutionalists", there's nothing in the constitution about marriage same sex or otherwise.
Ireland just became the first country to legalize same-sex marriage by a national vote—rather than through legislation or the courts.
The list of 21 countries where same-sex marriage is legal nationwide and the year it was approved (Mexico and the United States are not included, since they only allow same-sex marriage in certain jurisdictions):
The Netherlands (2000)
South Africa (2006)
England and Wales (2013)
New Zealand (2013)
Finland: (signed 2015, effective 2017)