ada assignment to in mode parameter not allowed

This is by design. A formal parameter of mode in is a constant view; it cannot be updated within the subprogram body. A constant cannot be the target of an assignment operation. See section 3.3 od Ada Reference Manual, paragraphs 13, 15, 17 and 25 in particular.

test_update.adb:11:09: error: assignment to "in" mode parameter not allowed test_update.adb:28:59: error: unexpected argument for "Access" attribute When I use the code in the comments, and remove the second parameter for the function, it still doesn't work.

2. You cannot assign a read-only variable. When you learn about Ada, you are taught that parameters are passed as copy when you are using the in keyword. The fact is that the compiler can decide to pass the parameter by reference and therefore it views the variable as a read-only variable. You cannot write in that variable.

The copy back of an [in] out mode parameter of a by-copy type only occurs on normal return from the subprogram [ARM 6.4.1(17)]. If the subprogram propagates an exception, the copy back does not occur, and the variable retains its original value. Both GNAT 12.3.0 and ObjectAda 10.5U5 behave this way.

1. [A parameter_specification declares a formal parameter of mode in, in out, or out .] Static Semantics. 2. A parameter is passed either by copy or by reference. [When a parameter is passed by copy, the formal parameter denotes a separate object from the actual parameter, and any information transfer between the two occurs only before and ...

A parameter of a by-copy type is passed by copy, unless the formal parameter is explicitly aliased. 4. A type is a by-reference type if it is a descendant of one of the following: 5. a tagged type; 6. a task or protected type; 7/3. { AI05-0096-1 } an explicitly limited record typea nonprivate type with the reserved word limited in its declaration;

A generic formal object of mode in is like a constant initialized to the value of the explicit_generic_actual_parameter. 1.b. ... Mode out is not allowed for generic formal objects. 7. ... (The part about denoting a variable, and renaming being allowed, is most certainly not a Name Resolution Rule.) 8/2

2. A parameter is passed either by copy or by reference. When a parameter is passed by copy, the formal parameter denotes a separate object from the actual parameter, and any information transfer between the two occurs only before and after executing the subprogram. When a parameter is passed by reference, the formal parameter denotes (a view ...

assignment to "in" mode parameter not allowed: 2011/02/02 : attribute "unchecked_access" cannot be applied to a subprogram: 2011/02/01 "end loop;" expected for "loop" at line <number> ... Another excellent resource about Ada is the Ada FAQ on the faqs website: Ada FAQ: Programming with Ada (part 1 of 4). Latest Edits. 3.6 Array Types.

By showing the mode of parameters, you aid the reader. If you do not specify a parameter mode, the default mode is in. Explicitly showing the mode indication of all parameters is a more assertive action than simply taking the default mode. Anyone reviewing the code later will be more confident that you intended the parameter mode to be in. Use ...

23. An in parameter can be read but not written by the subprogram. in is the default. Prior to Ada 2012, functions were only allowed to have in parameters. The actual parameter is an expression. An out parameter implies that the previous value is of no interest. The subprogram is expected to write to the parameter.

54 Assignment to a discriminant of an object (after its initialization) is not allowed, since the name of a discriminant is a constant; neither assignment_statement s nor assignments inherent in passing as an in out or out parameter are allowed. Note however that the value of a discriminant can be changed by assigning to the enclosing object ...

NOTE 1 { AI12-0056-1 } The mode of a formal parameter describes the direction of information transfer to or from the subprogram_body (see 6.1 ). NOTE 2 A formal parameter of mode in is a constant view (see 3.3 ); it cannot be updated within the subprogram_body.

Name Resolution Rules. 2. The formal_parameter_ selector_name of a parameter_association shall resolve to denote a parameter_specification of the view being called. 3. {actual parameter (for a formal parameter)} The actual parameter is either the explicit_actual_parameter given in a parameter_association for a given formal parameter, or the ...

Such reading and updating rights are specified by the mode of the formal parameter. Three parameter modes are provided in Ada: they are the modes in, in out, and out. The properties of formal parameters of each of these modes are summarized in the table given below. The second column indicates the nature of the formal parameter: constant or ...

I thought it should be rejected during compilation because in mode parameter is not allowed in an assignment statement. But, it was compiled successfully under GNAT obviously. ... parameter is not allowed in an assignment statement. But, it was compiled successfully under GNAT obviously. ... That Ada access types allow for implicit dereference ...

The main topic here is the fact that functions (but not operators) in Ada 2012 can have parameters of any mode. This is a topic left over from Ada 2005. The epilogue to the Rationale for Ada 2005 ... Calls to value returning procedures are only allowed in assignment statements, initializations and procedure calls. ...

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Syntax. 2. assignment_statement ::=. variable_ name := expression; 3. The execution of an assignment_statement includes the evaluation of the expression and the assignment of the value of the expression into the target. [An assignment operation (as opposed to an assignment_statement) is performed in other contexts as well, including object ...

In your if condition block, you are setting variable to null and it happens to be your method parameter. Instead of assigning the value to the method parameter, create a local variable and use it and return the value of the local variable from the method if at all it is intended.