Philosophy.__of__(Acquisition).questions
I thought I understood Acquisition, until I read the docs at http://www.digicool.com/releases/ExtensionClass/Acquisition.html. *Really* read them, until my brain hurt, then I went and had a lie down, then tried again. Now I'm *really* confused! Let me take the example from the docs: We have a tree that includes paths a/x and a/b/c. Whenever we ask an object which supports acquisition for an attribute which turns out to support acquisition, we are given a wrapper which preserves the context. Using 'of' to mean 'in the context of', the general transformation rule is (path/top/attr) -> (path/attr) of (path/top) if attr is not an element of top, or (path/attr) -> (attr of path) if it is. Here are some access paths and the resulting wrapper objects: a/b b of a a/b/c c of (a/b) -> c of (b of a) a/x x of a a/b/x (a/x) of (a/b) -> (x of a) of (b of a) a/b/c/x (a/b/x) of (a/b/c) -> ((a/x) of (a/b)) of (a/b/c) -> ((x of a) of (b of a)) of (c of (b of a)) Once a wrapper is written in 'of' notation, you can read off the acquisition order from left to right, skipping repeats. Thus, for 'a/b/c', the acquisition order is c, b , a, while for 'a/b/c/x' it is x, a, b, c. The addition of x reverses the acquisition sequence for the previous step! If x were contained in b instead, then we would have a/b/c/x -> (a/b/x) of (a/b/c) -> (x of b of a) of (c of b of a), giving sequence x, b, a, c!! This seemed horribly unintuitive to me, since I thought that an acquired object was only given the context of the object which started the acquisition search. This would lead to the same result for 'a/b/c', but 'a/b/c/x' would give x, c, b, a. Jim Fulton kindly explained, in another thread, how the acquired object's context is searched before the acquiring object's. Fine, that's fully consistent with all of the above. Now I try it out in Zope. I make nested folders 'a/b/c' in the root. I put DTML method 'x' in 'a', and have it display <dtml-var prop>. I give a, b, and c properties named 'prop', containing 'a!', 'b!', and 'c!' respectively. I call '/a/b/c/x' and it prints 'c!' What the hell? According to the docs, shouldn't it print 'a!'? Ok, let's try making DTML Method y in c with body "<dtml-var x>". Same result. How about "<dtml-with x><dtml-var prop></dtml-with>"? Same thing. Help??
On Sun, 26 Sep 1999, Evan Simpson wrote:
I call '/a/b/c/x' and it prints 'c!'
What the hell? According to the docs, shouldn't it print 'a!'?
Ok, let's try making DTML Method y in c with body "<dtml-var x>". Same result. How about "<dtml-with x><dtml-var prop></dtml-with>"? Same thing.
Help??
Your logic is correct. Just use DTML Document instead of DTML Method. DTML Method is an 'attribute' of the containing object not a subobject. If I remember correctly one of the reasons DTML Document was introduced was to enable exactly what you descriped. Pavlos
At 22:28 26-9-99 , Evan Simpson wrote:
I thought I understood Acquisition, until I read the docs at http://www.digicool.com/releases/ExtensionClass/Acquisition.html.
*Really* read them, until my brain hurt, then I went and had a lie down, then tried again.
Now I'm *really* confused! Let me take the example from the docs:
We have a tree that includes paths a/x and a/b/c. Whenever we ask an object which supports acquisition for an attribute which turns out to support acquisition, we are given a wrapper which preserves the context. Using 'of' to mean 'in the context of', the general transformation rule is (path/top/attr) -> (path/attr) of (path/top) if attr is not an element of top, or (path/attr) -> (attr of path) if it is.
Here are some access paths and the resulting wrapper objects:
a/b b of a a/b/c c of (a/b) -> c of (b of a) a/x x of a a/b/x (a/x) of (a/b) -> (x of a) of (b of a) a/b/c/x (a/b/x) of (a/b/c) -> ((a/x) of (a/b)) of (a/b/c) -> ((x of a) of (b of a)) of (c of (b of a))
Once a wrapper is written in 'of' notation, you can read off the acquisition order from left to right, skipping repeats. Thus, for 'a/b/c', the acquisition order is c, b , a, while for 'a/b/c/x' it is x, a, b, c.
The addition of x reverses the acquisition sequence for the previous step! If x were contained in b instead, then we would have a/b/c/x -> (a/b/x) of (a/b/c) -> (x of b of a) of (c of b of a), giving sequence x, b, a, c!!
This seemed horribly unintuitive to me, since I thought that an acquired object was only given the context of the object which started the acquisition search. This would lead to the same result for 'a/b/c', but 'a/b/c/x' would give x, c, b, a.
Jim Fulton kindly explained, in another thread, how the acquired object's context is searched before the acquiring object's. Fine, that's fully consistent with all of the above.
Now I try it out in Zope. I make nested folders 'a/b/c' in the root. I put DTML method 'x' in 'a', and have it display <dtml-var prop>. I give a, b, and c properties named 'prop', containing 'a!', 'b!', and 'c!' respectively.
I call '/a/b/c/x' and it prints 'c!'
What the hell? According to the docs, shouldn't it print 'a!'?
Ok, let's try making DTML Method y in c with body "<dtml-var x>". Same result. How about "<dtml-with x><dtml-var prop></dtml-with>"? Same thing.
Help??
Now make it a DTML Document =). See? -- Martijn Pieters, Web Developer | Antraciet http://www.antraciet.nl | T: +31 35 7502100 F: +31 35 7502111 | mj@antraciet.nl http://www.antraciet.nl/~mj | PGP: http://wwwkeys.nl.pgp.net:11371/pks/lookup?op=get&search=0xA8A32149 ---------------------------------------------
participants (3)
-
Evan Simpson -
Martijn Pieters -
Pavlos Christoforou