We have now enough experience to know that a type is defined to be used in variables declaration.
Let's see how to do it (simple) and how to manage them (less simple but not impossible):
... John,Mary,Smith : TPlayer; ... John.Name:='John Dangerous'; SetLength(John.Cards, Length(John.Cards)+4 ); //John has 4 cards John.Cards.Suit:=Spades; John.Cards.Rank:=Ten; John.Cards.Suit:=Hearts; John.Cards.Rank:=Ace; John.Cards.Suit:=Diamonds; John.Cards.Rank:=Two; John.Cards.Suit:=Diamonds; John.Cards.Rank:=Seven;
By using a dot we get access to record's items, with this scheme:
that can be iterative, just like in example above.
In facts a TPlayer is record whose items are:
- one string;
- one record, the TCard we talked about.
If we want to access to a value to the suit of cards of John, we must write:
which we can read as "John, who has some cards, the i-th which can have one possible value among Suit ones".
In code above we access only to assign values.
Now take a look to this code line:
String1 := GetEnumName(TypeInfo(TSuit),integer(John.Cards.Suit));
GetEnumName is a function, resulting in a string. Its arguments are two:
- a string;
- an integer.
It's interesting to understand how these values are reached.
The first with the TypeInfo function that returns the address where TypeInfo record is "placed": the address is called pointer, an important concept we'll talk about in future.
The second with a casting operation, which you can promote a type to another with (where possible): this presumes that John.Cards.Suit has a value already assigned. In this case a string is cast to an integer, because that one occupies less memory space than this one.
At a quick look somebody could think that this function is meaningless, because it's enough to assign the card's value to String1.
Remember that an enumeration type is a predefined collection of constant strings (masks for ordinal numbers), so that it cannot be rewritten nor read just like a common variable:
// Compile Error!! Types incompatible!! // Trying to assign an enumerated value to a string variable String1 := John.Cards.Suit;
Wrong code above results in an error during compilation because of the try to assign an uncorrect type to a variable of a different one.
Players record has a Cards record which has two enumerated: Suit and Rank.
So GetEnumName does the right thing: it reaches the address of the enumerated type, and uses the integer cast string value of John.Cards.Suit to return the Suit string related to the integer found.
Last but not least:
// Error!! Not ordinal!! Type EnumType = (one, two, three, forty := 40, thirty := 30);
will result in an obvious error during compilation.