c# - How can I use Code Contracts to ensure that a non-blank, non-null val should always be returned from a method? -

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this code:

private static char getbarcodechecksumwithlegacycode(string barcodewithoutczechsum) {     contract.requires(!string.isnullorwhitespace(barcodewithoutczechsum));     contract.ensures(contract.result != null);     . . .

...doesn't compile ("operator '!=' cannot applied operands of type 'method group' , ''").

this fails same way:

contract.ensures(contract.valueatreturn != null);

how can enforce necessity of method returning result using code contracts?

update

if this:

contract.ensures(contract.result<char>() != '');

...it fails with, "empty character literal"

so way test returned char val being both non-null , non-empty:

contract.ensures(contract.result<char>() != null && contract.result<char>().tostring() != string.empty);

...or null check suffice?

btw, trying use valueatreturn instead of result gives me "no overload method 'valueatreturn' takes 0 arguments"

update 2

this code:

contract.ensures(contract.result<string>() != null && contract.result<string>() != string.empty);

fails with:

in method barcodeczechdigittester.form1.getbarcodechecksumwithlegacycode(system.string): detected call result 'system.string', should 'system.char'.

(twice) also: "the command ""c:\program files (x86)\microsoft\contracts\bin\ccrewrite.exe" "@barcodeczechdigittesterccrewrite.rsp"" exited code 2."

...but changing code works:

contract.ensures(contract.result<char>() != null && contract.result<char>().tostring() != string.empty);

you need have like:

contract.ensures(contract.result<string>() != null);

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