I have made a declaration like this:
private const Complex I = new Complex(0.0, 1.0);
When I try to build this I get the error:
The expression being assigned to 'ComplexNumberL ib.ComplexMath. I' must be
constant.
I do not understand why this constructor is not considered to be constant
nor how
to correct this error. (Just learning C#)
Regards
Chris Saunders
15  3256 
Hi Chris,
a constant expression needs to be something that can be evaluated at
compile time, so you can only use consts with value types not reference types
(apart from string which is a little bit different and null).
If you want to have a non changeable reference type use the readonly keyword
instead.
Hope that helps
Mark Dawson http://www.markdawson.org
"Chris Saunders" wrote: I have made a declaration like this:
private const Complex I = new Complex(0.0, 1.0);
When I try to build this I get the error:
The expression being assigned to 'ComplexNumberL ib.ComplexMath. I' must be
constant.
I do not understand why this constructor is not considered to be constant
nor how
to correct this error. (Just learning C#)
Regards
Chris Saunders
Chris, I have made a declaration like this:
private const Complex I = new Complex(0.0, 1.0);
When I try to build this I get the error:
The expression being assigned to 'ComplexNumberL ib.ComplexMath. I' must be
constant.
A constant expression is an expression that can be fully evaluated at
compile time. Therefore, the only possible values for constants of reference
types are string and null.
Regards,
Randy
Did you write the code for Complex? If so, can you provide the code for the
constructor you're calling?
--
Dale Preston
MCAD C#
MCSE, MCDBA
"Chris Saunders" wrote: I have made a declaration like this:
private const Complex I = new Complex(0.0, 1.0);
When I try to build this I get the error:
The expression being assigned to 'ComplexNumberL ib.ComplexMath. I' must be
constant.
I do not understand why this constructor is not considered to be constant
nor how
to correct this error. (Just learning C#)
Regards
Chris Saunders
A constant expression is an expression that can be fully evaluated at
compile time. Therefore, the only possible values for constants of
reference types are string and null.
Possibly you need "readonly" field
And if you *did* write this code, then note that Complex should probably be
a value-type (struct), not a reference type (class); this would solve this
problem, plus allow for value-type symantecs, which is what people probably
expect from a complex (or quarternian for that matter) number.
Marc
Even if Compex type shall be changed from "class" to "struct" it will
not solve the problem.
Constant expression is evaluated in compile time and embedded into IL
code and it is impossible for complex data structures
C# language specification
7.15 Constant expressions
A constant-expression is an expression that can be fully evaluated at
compile-time.
constant-expression:
expression
The type of a constant expression can be one of the following: sbyte,
byte, short, ushort, int, uint, long, ulong, char, float, double,
decimal, bool, string, any enumeration type, or the null type
My thanks for the many responses.
Particularily Vladimir Matveev since you led me to
the specification - which I will read.
I have just been learning C# for a couple of days now
and was just writing the Complex class as a way to
learn.
One person suggested that I should use a struct and I
will give that option a try - don't know C# well enough
yet to understand the implications.
I am mostly accustomed to Eiffel which is quite different -
in Eiffel you can make a class a value type.
Anyways, many thanks for the help.
Regards
Chris Saunders
Fair enough;
</retract> ;-p
Marc
Phew... you saved my dignity there by vindicating at least *part* of my
previous post ;-p
IMO, yes, you should be using a struct for this; an alternative would be an
*immutable* class (e.g. one where all the fields are formally readonly and
the class is marked [Immutable]) - otherwise you could get some very
unexpected results, particularly if two objects have a Complex property, and
the same Complex instance is assigned to both; when one of them updates the
object (e.g. adds 2 to the real part), then the value would appear to change
for *both* objects that hold it, which is probably not what is intended.
Marc
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