{"id":5244,"date":"2014-03-30T20:00:32","date_gmt":"2014-03-30T20:00:32","guid":{"rendered":"https:\/\/unknownerror.org\/index.php\/2014\/03\/30\/can-dependency-injection-prevent-a-circular-dependency-collection-of-common-programming-errors\/"},"modified":"2014-03-30T20:00:32","modified_gmt":"2014-03-30T20:00:32","slug":"can-dependency-injection-prevent-a-circular-dependency-collection-of-common-programming-errors","status":"publish","type":"post","link":"https:\/\/unknownerror.org\/index.php\/2014\/03\/30\/can-dependency-injection-prevent-a-circular-dependency-collection-of-common-programming-errors\/","title":{"rendered":"Can dependency injection prevent a circular dependency?-Collection of common programming errors"},"content":{"rendered":"

You probably could<\/em> solve this with DI, but you shouldn’t<\/em>.<\/p>\n

If I understand correctly, you have something like this:<\/p>\n

\n  + Assembly A           + Assembly B\n  |                      |\n  +-- Interface IFoo     +-- Class ConcreteFoo : IFoo\n  |                                   ^\n  +-- Class MyClass -->------->-------|\n<\/pre>\n
In other words, you’re trying to get MyClass<\/code> to reference ConcreteFoo<\/code>, but you can’t because assembly B<\/code>, which ConcreteFoo<\/code> resides in, already depends on IFoo<\/code> in A<\/code>.<\/p>\n
This is a design error. If you declare the interface IFoo<\/code> in Assembly A<\/code>, but no concrete implementations, then any other interfaces\/classes in assembly A<\/code> should only<\/strong> reference IFoo<\/code>, never<\/strong> a concrete class that implements it.<\/p>\n
There are three ways to eliminate the circular dependency:<\/p>\n
    \n
  1. \n
    Make MyClass<\/code> dependent on IFoo<\/code> instead of ConcreteFoo<\/code>. This is probably the best option if you can do it. If the issue is that you need a physical instance of IFoo<\/code> for use in MyClass<\/code> and don’t know where to get one from, then have it take an IFoo<\/code> in the constructor – let whoever uses MyClass<\/code> figure out what IFoo<\/code> to use.<\/p>\n<\/li>\n
  2. \n
    Move the interfaces to their own assembly. This is still a reasonably good practice. Your design will look like this:<\/p>\n<\/li>\n<\/ol>\n
      + Assembly App       + Assembly Interfaces      + Assembly Concrete\n      |                    |                          |\n      |                    +-- Interface IFoo         |\n      |                    |                  \\       |\n      +-- Class MyClass    |                   \\------+-- Class ConcreteFoo\n      |                    |                          |           ^\n      +---- Member Foo ->--------------------->-------------------|\n  <\/pre>\n
      \n
    1. Move MyClass<\/code> to its own assembly. Effectively your dependency tree will look the same as in #2 above, but if assembly A<\/code> is much smaller than B<\/code> then this would require less effort.<\/li>\n<\/ol>\n
      Hope that helps.<\/p>\n","protected":false},"excerpt":{"rendered":"
      You probably could solve this with DI, but you shouldn’t. If I understand correctly, you have something like this: + Assembly A + Assembly B | | +– Interface IFoo +– Class ConcreteFoo : IFoo | ^ +– Class MyClass –>——->——-| In other words, you’re trying to get MyClass to reference ConcreteFoo, but you can’t […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-5244","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/5244","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/comments?post=5244"}],"version-history":[{"count":0,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/posts\/5244\/revisions"}],"wp:attachment":[{"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/media?parent=5244"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/categories?post=5244"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/unknownerror.org\/index.php\/wp-json\/wp\/v2\/tags?post=5244"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}