Title: Iterating Over a Set type Variable in Delphi - Using For .. In Set_Values
Delphi's set type is one of the features of the language commonly not found in other programming languages. Sets represent a collection of values of the same ordinal type.
A commonly used scenario in Delphi code is to mix both enumerated types and set type.
Here's an example:
type
TWorkDay = (Monday, Tuesday, Wednesday, Thursday, Friday) ;
...
const
FirstShift = [Monday, Wednesday, Friday];
Looping Through a Set
If you need to iterate through the elements of a set, you can use the *new* for .. in Delphi loop:
const
FirstShift = [Monday, Wednesday, Friday];
SecondShift = [Tuesday, Thursday];
var
aDay : TWorkDay;
begin
for aDay in FirstShift do
begin
//do something for
//Monday, Wednesday, Friday
{once for each element}
end
end;
But what if you want to go through every possible value in a set?
Take a look at the next example...
var
character : 'a' .. 'z';
begin
for character in [Low(character) .. High(character)] do
begin
ShowMessage(character) ;
end;
end;
What will the message display? How many times the message will be displayed?
Answer: the message box will display lower case letters from 'a' to 'z' - 26 characters (English "version")!
Note: Low function returns the smallest available value for a range.
High function returns the upper limit of an Ordinal, Array, or ShortString value.
"Homework" 1:
Let's say you have a label control on a form named "Label1". What will be the result of the code:
var
fs : TFontStyle;
begin
for fs in [Low(fs) .. High(fs)] do
Label1.Font.Style := Label1.Font.Style + [fs];
end;
Hint: try it :))
"Homework" 2
Given the next code, what will the message box display?
type
TCharSet = set of char;
var
character : 'a'..'z';
charSet : TCharSet;
phrase : string;
begin
charSet := [];
for character in [Low(character) .. High(character)] do
begin
if character in ['d', 'e', 'l', 'p', 'h', 'i'] then
begin
Include(charSet, character) ;
end;
end;
for character in charSet do
begin
phrase := phrase + character;
end;
ShowMessage(phrase) ;
end;
Answer : "dehilp" :)
Clearing the Confusion: Set, Range, Sub Range, Enumeration
In the above example:
"TCharSet" is a character set type - variables of this type can hold character elements - a collection of characters,
variable "character" is a subrange variable - can hold any (one) character between (lower-cased) 'a' and 'z',
"charSet" is a character set type variable - can hold a collection (set) of any ASCII characters,
"word" - is an ordinary string variable.