Lazarus – ways to extract values from an enumeration

Hello, guys! We're continuing to master Lazarus. It's a wonderful programming language similar to Delphi. There's a data type called an enumeration. And sometimes we want to extract values from it. Here's a funny question: How do we do this? We'll look at that today.

Let's create a standard project in Lazarus. With a Windows window. In the TYPE section, we'll add our enumeration. Let's say it's the seasons of the year: Autumn, Winter, Spring, Summer.

ESeason = (Autumn, Winter, Spring, Summer);

Method 1. WriteStr. The simplest.

And here's the simplest method. It's using WriteStr. We write the desired enumeration type element into a string.

Var

MySeason: ESeason;

StrVal:String;

begin

WriteStr(StrVal,MySeason);

Memo1.Lines.Add('MySeason=' + StrVal);

WriteStr(StrVal,Winter);

Memo1.Lines.Add(Winter=' + StrVal);

WriteStr(StrVal,ESeason.Spring);

Memo1.Lines.Add('ESeason.Spring=' + StrVal);

End;

Our StrVal text variable can hold a wide variety of enumeration values. This is all possible! Quite flexible and variable! Notice how many possibilities there are. You can pass a variable of an enumeration type, like MySeason. You can also pass one of the enumeration elements directly by name, like Winter. And you can pass one of the enumeration values with the full name, as expected. The enumeration type and its specific value separated by a dot. For example, ESeason.Spring.

Method 2. GetEnumName (), Ord(). More complicated.

First, we include TypInfo in Uses.

And here's an important detail. TypeInfo doesn't work if enumerations have assigned numeric values.

For example, if an enumeration is defined like this:

ESeason2 = (Autumn=1, Winter, Spring, Summer); //typeinfo doesn't work when there are numeric values!

So, we're continuing to work with our enumeration from the beginning. This will work:

ESeason = (Autumn, Winter, Spring, Summer);

Now let's move on to the code. Extracting a value from the enumeration is done in several steps.

Preliminary detail. We obtain the numeric equivalent of the value via Ord().

Ord(MySeason)

Preliminary detail. We obtain information about our enumeration. Via TypeInfo.

TypeInfo(ESeason)

And we do everything through the conversion operator. Convert to a string using GetEnumType

StrVal:= GetEnumType(TypeInfo(ESeason),Ord(MySeason))

Pass the type of our enumeration to GetEnumType. This is ESeason. And the numeric value we're interested in is MySeason.

IntVal:=ord(MySeason);

Example Program

var

MySeason:ESeason;

IntVal: integer;

StrVal:String;

begin

StrVal:=GetEnumName(TypeInfo(ESeason),ord(MySeason));

Memo1.Lines.Add('MySeason Integer value = ' + IntToStr(IntVal));

Memo1.Lines.Add('MySeason String value = ' + StrVal);

IntVal:=Ord(Winter);

StrVal:=GetEnumName(TypeInfo(ESeason),ord(Winter));

Memo1.Lines.Add('Winter Integer - ' + IntToStr(IntVal));

Memo1.Lines.Add('Winter String - ' + StrVal);

IntVal:=Ord(ESeason.Spring);

StrVal:=GetEnumName(TypeInfo(ESeason),ord(ESeason.Spring));

Memo1.Lines.Add('ESeason.Spring Integer - ' + IntToStr(IntVal));

Memo1.Lines.Add('ESeason.Spring String - ' + StrVal);

End;

Method 3. Manually assigning values. The most sophisticated method.

To do this, we'll create a chain. We'll also write the identifiers into a string array.

This still works as a constant. And with ESeason.

const MySeasonNames: Array[ESeason] of string =('Autumn','Winter','Spring','Summer');

Let me remind you that the enumeration itself looks like this:

ESeason = (Autumn, Winter, Spring, Summer);

We're essentially associating the enumeration with a special array. In the array, all values are written as strings.

Now we can access this array by passing the enumeration value as an array index.

For example, like this

StrVal:=MySeasonNames[MySeason];

Or like this

StrVal:=MySeasonNames[Winter];

Or like this

StrVal:=MySeasonNames[ESeason.Spring];

We've sort of mapped the array, associating it with the enumeration elements. A clever move. And now we access our map. By throwing enumeration values into an array. The array index is the enumeration value.

Var

MySeason:ESeason;

IntVal: integer;

StrVal: String;

begin

StrVal:=MySeasonNames[MySeason];

Memo1.Lines.Add('MySeason =' + StrVal);

StrVal:=MySeasonNames[Winter];

Memo1.Lines.Add('Winter - ' + StrVal);

StrVal:=MySeasonNames[ESeason.Spring];

Memo1.Lines.Add('MySeason.Spring - ' + StrVal);

End;

Those are three such methods! Delphi is interesting! Let's learn, guys! I'm learning too! And I'm learning everything gradually. Sometimes I spend a lot of time even on a couple of lines of code.