{"action":"created","issue":{"url":"https://api.github.com/repos/p4lang/p4c/issues/1236","repository_url":"https://api.github.com/repos/p4lang/p4c","labels_url":"https://api.github.com/repos/p4lang/p4c/issues/1236/labels{/name}","comments_url":"https://api.github.com/repos/p4lang/p4c/issues/1236/comments","events_url":"https://api.github.com/repos/p4lang/p4c/issues/1236/events","html_url":"https://github.com/p4lang/p4c/issues/1236","id":315704028,"number":1236,"title":"Why not allow to use variable for Header Stack's pop_front() Now?","user":{"login":"MaoJianwei","id":12800168,"avatar_url":"https://avatars2.githubusercontent.com/u/12800168?v=4","gravatar_id":"","url":"https://api.github.com/users/MaoJianwei","html_url":"https://github.com/MaoJianwei","followers_url":"https://api.github.com/users/MaoJianwei/followers","following_url":"https://api.github.com/users/MaoJianwei/following{/other_user}","gists_url":"https://api.github.com/users/MaoJianwei/gists{/gist_id}","starred_url":"https://api.github.com/users/MaoJianwei/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/MaoJianwei/subscriptions","organizations_url":"https://api.github.com/users/MaoJianwei/orgs","repos_url":"https://api.github.com/users/MaoJianwei/repos","events_url":"https://api.github.com/users/MaoJianwei/events{/privacy}","received_events_url":"https://api.github.com/users/MaoJianwei/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":4,"created_at":"2018-04-19T02:19:25Z","updated_at":"2018-04-19T15:28:02Z","closed_at":null,"author_association":"NONE","body":"Hi,\r\n\r\nIn the version of several months ago of p4c , I can use a variable in header as a arg of pop_front(), as follow.\r\n\r\nWhy not allow to use variable for Header Stack's pop_front() now ?\r\n\r\n![qq 20180419101538](https://user-images.githubusercontent.com/12800168/38967764-1eb712de-43bb-11e8-8677-51dd939239c8.png)\r\n\r\n\r\nThanks!"},"comment":{"url":"https://api.github.com/repos/p4lang/p4c/issues/comments/382778737","html_url":"https://github.com/p4lang/p4c/issues/1236#issuecomment-382778737","issue_url":"https://api.github.com/repos/p4lang/p4c/issues/1236","id":382778737,"user":{"login":"mbudiu-vmw","id":19397042,"avatar_url":"https://avatars1.githubusercontent.com/u/19397042?v=4","gravatar_id":"","url":"https://api.github.com/users/mbudiu-vmw","html_url":"https://github.com/mbudiu-vmw","followers_url":"https://api.github.com/users/mbudiu-vmw/followers","following_url":"https://api.github.com/users/mbudiu-vmw/following{/other_user}","gists_url":"https://api.github.com/users/mbudiu-vmw/gists{/gist_id}","starred_url":"https://api.github.com/users/mbudiu-vmw/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/mbudiu-vmw/subscriptions","organizations_url":"https://api.github.com/users/mbudiu-vmw/orgs","repos_url":"https://api.github.com/users/mbudiu-vmw/repos","events_url":"https://api.github.com/users/mbudiu-vmw/events{/privacy}","received_events_url":"https://api.github.com/users/mbudiu-vmw/received_events","type":"User","site_admin":false},"created_at":"2018-04-19T15:28:02Z","updated_at":"2018-04-19T15:28:02Z","author_association":"COLLABORATOR","body":"The point of P4 is not to be a general-purpose programming language, but to allow people to program a large variety of switching devices. There are some ASIC devices which hold header stacks in registers. For these there is no way to efficiently implement pop/push with a non-constant number of arguments. There are many other such limitations in P4, e.g., indexing an array with a non-constant value is not supported on many targets. Loops are not supported. "}}
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