Function with return type boolean

Question

I have created a function with return type boolean as:
CREATE OR REPLACE FUNCTION fn RETURN BOOLEAN
AS
exp EXCEPTION;
BEGIN
return TRUE;
EXCEPTION
when OTHERS then RAISE exp;
END;
FUNCTION fn compiledThen I was trying to call this function into dbms_output.put_line procedure, I got this error:
EXECUTE DBMS_OUTPUT.PUT_LINE(fn);
ORA-06550: line 1, column 7:
PLS-00306: wrong number or types of arguments in call to 'PUT_LINE'Can someone please help me understand, why this happened?
Is this because of boolean return type?

Answer 1

952040 wrote:
I have created a function with return type boolean as:
Then I was trying to call this function into dbms_output.put_line procedure, I got this error:
EXECUTE DBMS_OUTPUT.PUT_LINE(fn);
ORA-06550: line 1, column 7:
PLS-00306: wrong number or types of arguments in call to 'PUT_LINE'
What is the parameter signature for DBMS_OUTPUT.put_line() ?
Is is string - as detailed in Oracle® Database PL/SQL Packages and Types Reference guide.
So how can you pass a boolean data type as parameter value, when the parameter's data type is string?
PL/SQL supports implicit data conversion. So you can for example pass a number or date value to DBMS_OUTPUT.put_line() - and the PL/SQL engine automatically (and implicitly) converts that (using the TO_CHAR() functions) to a string.
However, the TO_CHAR() parameter signature supports number and date - not boolean. It cannot convert a boolean value into a string.
So passing a boolean value means the implicit conversion fails - and results in the above error.
To make it work, you need to perform an explicit conversion. As as a data type conversion function from boolean to string is not available, you need to write a user defined function. E.g.
SQL> create or replace function BoolToChar( b boolean ) return varchar2 is
  2  begin
  3    case
  4       when b then return( 'TRUE' );
  5       when not b then return( 'FALSE' );
  6    else
  7      return( null );
  8    end case;
  9  end;
10  /
Function created.
SQL>
SQL> exec DBMS_OUTPUT.put_line( 'Flag is '||BoolToChar(true) );
Flag is TRUE
PL/SQL procedure successfully completed