{"id":17576,"date":"2022-10-25T20:44:56","date_gmt":"2022-10-25T15:14:56","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-how-is-transforming-this-iterator-block-a-functional-change\/"},"modified":"2022-10-25T20:44:56","modified_gmt":"2022-10-25T15:14:56","slug":"solved-how-is-transforming-this-iterator-block-a-functional-change","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-how-is-transforming-this-iterator-block-a-functional-change\/","title":{"rendered":"[Solved] How is transforming this iterator block a functional change?"},"content":{"rendered":"

[ad_1]
\n<\/p>\n

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\n
<\/div>\n
\n
\n

The two are not equivalent. The semantics of how execution is deferred between the two Bar<\/code> methods is different. Foo.Bar<\/code> will evaluate Sequence<\/code> into an IEnumerable<\/code> value when you call Bar<\/code><\/em>. Foo2.Bar2<\/code> will evaluate Sequence<\/code> into the value in that variable when you enumerate the sequence returned by Bar2<\/code><\/em>.<\/p>\n

We can write a simple enough program to observe the differences here.<\/p>\n

\/\/Using iterator block\nvar foo = new Foo();\nfoo.Sequence = new[] { \"Old\" };\nvar query = foo.Bar();\nfoo.Sequence = new[] { \"New\" };\nConsole.WriteLine(string.Join(\" \", query));\n\n\/\/Not using iterator block\nvar foo2 = new Foo2();\nfoo2.Sequence = new[] { \"Old\" };\nvar query2 = foo2.Bar2();\nfoo2.Sequence = new[] { \"New\" };\nConsole.WriteLine(string.Join(\" \", query2));\n<\/code><\/pre>\n
This prints out:<\/p>\n
\n
New
\n  Old<\/p>\n<\/blockquote>\n
In this particular case our Bar<\/code> method also has no side effects.  If it did it would not be noticeably more important to understand the semantics that your program has, and what it should have.  For example, let’s modify the two methods so that they have some observable side effects:<\/p>\n
public class Foo\n{\n    public IEnumerable<string> Sequence { get; set; }\n    public IEnumerable<string> IteratorBlock()\n    {\n        Console.WriteLine(\"I'm iterating Sequence in an iterator block\");\n        foreach (string s in Sequence)\n            yield return s;\n    }\n    public IEnumerable<string> NoIteratorBlock()\n    {\n        Console.WriteLine(\"I'm iterating Sequence without an iterator block\");\n        return Sequence;\n    }\n}\n<\/code><\/pre>\n
Now let’s try comparing these two methods to see how they function:<\/p>\n
var query = foo.IteratorBlock();\nvar query2 = foo.NoIteratorBlock();\nConsole.WriteLine(\"---\");\nquery.Count();\nquery.Count();\nquery2.Count();\nquery2.Count();\n<\/code><\/pre>\n
This will print out:<\/p>\n
\n
I’m iterating Sequence without an iterator block
\n  —
\n  I’m iterating Sequence in an iterator block
\n  I’m iterating Sequence in an iterator block<\/p>\n<\/blockquote>\n
Here we can see that the non-iterator block’s side effects happen when the method itself is called<\/em>, and the iterator block’s side effects don’t happen at that point in time.  Then, later on, each time we iterate the non-iterator block it doesn’t cause the side effects at all, but the iterator block causes the side effects each time the query is iterated<\/em>.<\/p>\n<\/p><\/div>\n
<\/div>\n<\/div>\n
            6<\/span> <\/p><\/div>\n<\/div>\n
[ad_2]<\/p>\n
solved How is transforming this iterator block a functional change? <\/p>\n","protected":false},"excerpt":{"rendered":"
[ad_1] The two are not equivalent. The semantics of how execution is deferred between the two Bar methods is different. Foo.Bar will evaluate Sequence into an IEnumerable value when you call Bar. Foo2.Bar2 will evaluate Sequence into the value in that variable when you enumerate the sequence returned by Bar2. We can write a simple … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324,4348,350,4347],"class_list":["post-17576","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c","tag-deferred-execution","tag-iterator","tag-yield-return"],"yoast_head":"\n[Solved] How is transforming this iterator block a functional change? - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-how-is-transforming-this-iterator-block-a-functional-change\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] How is transforming this iterator block a functional change? - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] The two are not equivalent. 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