class properties as per-type cache

MetaClassCache.dpr

program MetaClassCache;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.TypInfo,
  System.SysUtils;

type
  TypeInfoCache<T> = class
  class var
    FMinIntVal: Integer;
    FMaxIntVal: Integer;
  public
    class constructor Create;
    class property MaxIntVal: Integer read FMaxIntVal;
    class property MinIntVal: Integer read FMinIntVal;
  end;

  Range<T> = record
  private
    class function MaxIntVal: Integer; static; inline;
    class function MinIntVal: Integer; static; inline;
  public
    class function Check(const value: Integer): T; static;
  end;

{ Range<T> }

class function Range<T>.Check(const value: Integer): T;
begin
  if (value < MinIntVal) or (value > MaxIntVal) then
    raise Exception.CreateFmt('Value %d lies outside allowed range for %s (%d .. %d)',
      [value, PTypeInfo(TypeInfo(T)).Name, MinIntVal, MaxIntVal]);
end;

class function Range<T>.MaxIntVal: Integer;
begin
  Result := TypeInfoCache<T>.MaxIntVal;
end;

class function Range<T>.MinIntVal: Integer;
begin
  Result := TypeInfoCache<T>.MinIntVal;
end;

{ TypeInfoCache<T> }

class constructor TypeInfoCache<T>.Create;
var
  ti: PTypeInfo;
  typeData: PTypeData;
  isSet: Boolean;
  i: Integer;
begin
  ti := TypeInfo(T);
  isSet := ti.Kind = tkSet;
  if isSet then
    ti := GetTypeData(ti).CompType^;
  typeData := GetTypeData(ti);
  FMinIntVal := typeData.MinValue;

  if isSet then
  begin
    FMaxIntVal := 0;
    for i := typeData.MinValue to typeData.MaxValue do
      FMaxIntVal := FMaxIntVal or (1 shl i);
  end
  else
    FMaxIntVal := typeData.MaxValue;
end;

type
  TEnum = (en1, en2, en3);
  TEnumSet = set of TEnum;

var
  en: TEnum;
  ens: TEnumSet;

begin
  try
    en := Range<TEnum>.Check(0);
    en := Range<TEnum>.Check(2);
    try
      en := Range<TEnum>.Check(3);
    except
      on E: Exception do
        Writeln('Expected exception: ', E.ClassName, ' ', E.Message);
    end;

    ens := Range<TEnumSet>.Check(0);
    ens := Range<TEnumSet>.Check(7);
    try
      ens := Range<TEnumSet>.Check(8);
    except
      on E: Exception do
        Writeln('Expected exception: ', E.ClassName, ' ', E.Message);
    end;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
  if DebugHook <> 0 then
    Readln;
end.