.net - C# How to use FirstOrDefault with an array while unable to have System.Linq in the namespace? -

the code provided here works when test in ide, software using code doesn't give me possibility declare using system.linq. i'm stuck trying figure out how use else i'll have go solution i'd rather not use because has lower accuracy rate.

the issue here

var stringmatch = sarray.firstordefault(titleid.contains); 

i'm not sure how provide references. think should along ways of system.linq.enumerable... it's first time i'm dealing such issue appreciated.

        string takeendperiod = "";         string newendperiod = "";         string findendspace = "";         string getendperiod = "";         string titleid = "document period ended december 31 2014";          string s1 = "ended ";         string s2 = "ended ";         string s3 = "ending ";         string[] sarray = new [] { s1, s2, s3};                var stringmatch = sarray.firstordefault(titleid.contains);             if (stringmatch != null)             {                 takeendperiod = titleid.substring(titleid.lastindexof(stringmatch));                 findendspace = takeendperiod.substring(takeendperiod.indexof(" "));                 getendperiod = findendspace.substring(1);                 string[] formatarray = new[] { "dd mmmm yyyy", "mmmm dd yyyy" };                  datetime modendperiod;                 if (!datetime.tryparseexact(getendperiod,                                             formatarray,                                             system.globalization.cultureinfo.invariantculture,                                             system.globalization.datetimestyles.none,                                             out modendperiod))                 {                         //parsing failed                  }                  newendperiod = modendperiod.tostring("yyyy-mm-ddt00:00:00z"); 

edit:

error message i'm getting:

'system.array' not contain definition 'firstordefault' , no extension  method 'firstordefault' accepting first argument of type 'system.array'  found (are missing using directive or assembly reference?) 

edit:

this solution got dev support managing software:

string title = "document period ending december 31 2014";             match m = regex.match(title, ".*?(?i)(ended|ending)(.*)");//case insensitive search "ended" , "ending"             if (m.groups.count == 3)             {                 //match ok                 datetime dt = datetime.parse(m.groups[2].value);                 //the variable dt have parsed date.                 console.writeline(dt.tostring("yyyymmdd"));             } 

doesn't give me possibility declare 'using system.linq'.

since enumerable.firstordefault extension method can use it's qualified class-name system.linq.enumerable:

var stringmatch = system.linq.enumerable.firstordefault(sarray, s => titleid.contains(s)); 

or shorter:

var stringmatch = system.linq.enumerable.firstordefault(sarray, titleid.contains); 

note extension method static method, that's why works.

demo