function toString() {
			var out;
			var i;
			if ( this !== tuple ) { // eslint-disable-line no-invalid-this
				throw new TypeError( 'invalid invocation. `this` is not host tuple.' );
			}
			out = opts.name + '(';
			for ( i = 0; i < nfields; i++ ) {
				out += fields[ i ];
				out += '=';
				out += tuple[ indices[ i ] ];
				if ( i < nfields-1 ) {
					out += ', ';
				}
			}
			out += ')';
			return out;
		}
Serializes a tuple as a string.

@private
@memberof tuple
@throws {TypeError} `this` must be the host tuple
@returns {string} tuple string representation