The pointer to the stored values as OpenGL requires it. Note this will return a pointer to a row-major _matrix, this means you've to set the transpose argument to GL_TRUE when passing it to OpenGL. The current _matrix formatted as flat string.
// 3rd argument = GL_TRUE glUniformMatrix4fv(programs.main.model, 1, GL_TRUE, mat4.translation(-0.5f, -0.5f, 1.0f).value_ptr);