Asp Forum - [ANN] SuperStruct

Hal E. Fulton

11/17/2004 11:56:00 PM

Hello all...

In connection with things discussed here recently (re Struct and
OpenStruct), I've just released SuperStruct ("into the wild," as
Dan Berger would say).

Basically it allows you to create a Struct that is more classlike
and can be treated more like an Array and/or Hash, with a few
limitations. It creates accessors for each key, has predictable
instance var names, etc.

Whether it's truly useful remains to be seen. As Dave pointed out,
a class with a lot of accessors is not well encapsulated. You may
think this is worse than a Struct, but I like it better. YMMV.

See http://sstruct.rub... or the blurb below.

Thanks,
Hal Fulton

====================================================

SuperStruct
Hal Fulton
Version 1.0
License: The Ruby License

This is an easy way to create Struct-like classes; it converts easily
between hashes and arrays, and it allows OpenStruct-like dynamic naming
of members.

Unlike Struct, it creates a "real" class, and it has real instance variables
with predictable names.

A basic limitation is that the hash keys must be legal method names (unless
used with send()).

Basically, ss["alpha"], ss[:alpha], and ss.alpha all mean the same.

NOTES:

It's like a Struct...
- you can pass in a list of symbols for accessors
- it will create a class for you
but...
- you don't have to pass in the class name
- it returns a "real" class
. instance variables have the expected names
. you can reopen and add methods
- it doesn't go into the Struct:: namespace
- it preserves the order of the fields
- you can use Strings instead of Symbols for the names

It's like an Array...
- you can access the items by [number] and [number]=
but...
- you can also access the items by ["name"] and ["name"]=
- you can access the items by accessors

It's like an OpenStruct...
- (if you use .open instead of .new) you can add fields
automatically with x.field or x.field=val
but...
- you can initialize it like a Struct
- it preserves the order of the fields

It's like a Hash...
- data can be accessed by ["name"]
but...
- order (of entry or creation) is preserved
- arbitrary objects are not allowed (it does obj.to_str or obj.to_s)
- strings must be valid method names

It's like Ara Howard's Named Array...
- we can access elements by ["name"] or ["name"]=
but...
- you can access the items by accessors
- strings must be valid method names

It's like Florian Gross's Keyed List...
(to be done)
but...
- it preserves the order of the fields

Some examples: (see test cases)
--------------

# Need not assign to existing fields (default to nil)
myStruct = SuperStruct.new(:alpha)
x = myStruct.new
x.alpha # nil

# A value assigned at construction may be retrieved
myStruct = SuperStruct.new(:alpha)
x = myStruct.new(234)
x.alpha # 234

# Unassigned fields are nil
myStruct = SuperStruct.new(:alpha,:beta)
x = myStruct.new(234)
x.beta # nil

# An open structure may not construct with nonexistent fields
myStruct = SuperStruct.open
x = myStruct.new(234) # error

# An open structure may assign fields not previously existing
myStruct = SuperStruct.open
x = myStruct.new
x.foo = 123
x.bar = 456

# The act of retrieving a nonexistent field from an open struct will
# create that field
myStruct = SuperStruct.open
x = myStruct.new
x.foo # nil

# A field (in an open struct) that is unassigned will be nil
myStruct = SuperStruct.open
x = myStruct.new
y = x.foobar

# A struct created with new rather than open cannot reference nonexistent
# fields
myStruct = SuperStruct.new
x = myStruct.new
x.foo # error

# Adding a field to a struct will create a writer and reader for that field

# An open struct will also create a writer and a reader together

# A field has a real writer and reader corresponding to it

# A string will work as well as a symbol
myStruct = SuperStruct.new("alpha")

# to_a will return an array of values
myStruct = SuperStruct.new("alpha","beta","gamma")
x = myStruct.new(7,8,9)
assert(x.to_a == [7,8,9])

# Instance method 'members' will return a list of members (as strings)
myStruct = SuperStruct.new(:alpha,"beta")
x = myStruct.new
assert_equal(["alpha","beta"],x.members)

# Class method 'members' will return a list of members (as strings)
myStruct = SuperStruct.new(:alpha,"beta")
assert_equal(["alpha","beta"],myStruct.members)

# to_ary will allow a struct to be treated like an array in
# multiple assignment
myStruct = SuperStruct.new("alpha","beta","gamma")
x = myStruct.new(7,8,9)
a,b,c = x
assert(b == 8)

# to_ary will allow a struct to be treated like an array in
# passed parameters
myStruct = SuperStruct.new("alpha","beta","gamma")
x = myStruct.new(7,8,9)
b = meth(*x)

# to_hash will return a hash with fields as keys
myStruct = SuperStruct.new("alpha","beta","gamma")
x = myStruct.new(7,8,9)
h = x.to_hash
assert_equal({"alpha"=>7,"beta"=>8,"gamma"=>9},h)

# A field name (String) may be used in a hash-like notation
myStruct = SuperStruct.new("alpha","beta","gamma")
x = myStruct.new(7,8,9)
y = x["beta"]

# A field name (Symbol) may be used in a hash-like notation
myStruct = SuperStruct.new("alpha","beta","gamma")
x = myStruct.new(7,8,9)
y = x[:beta]

# [offset,length] may be used as for arrays
myStruct = SuperStruct.new("alpha","beta","gamma")
x = myStruct.new(7,8,9)
y = x[0,2]

# Ranges may be used as for arrays
myStruct = SuperStruct.new("alpha","beta","gamma")
x = myStruct.new(7,8,9)
y = x[1..2]

# Adding a field to an open struct adds it to the instance
myStruct = SuperStruct.open(:alpha)
x = myStruct.new
x.beta = 5

# Adding a field to an open struct adds it to the class also
myStruct = SuperStruct.open(:alpha)
x = myStruct.new
x.beta = 5

# An array passed to SuperStruct.new need not be starred
myStruct = SuperStruct.new(%w[alpha beta gamma])
x = myStruct.new

# A hash passed to #set will set multiple values at once
myStruct = SuperStruct.new(%w[alpha beta gamma])
x = myStruct.new
hash = {"alpha"=>234,"beta"=>345,"gamma"=>456}
x.set(hash)

# ||= works properly
x = SuperStruct.open.new
x.foo ||= 333
x.bar = x.bar || 444

# attr_tester will create a ?-method
myStruct = SuperStruct.new(:alive)
myStruct.attr_tester :alive
x = myStruct.new(true)
x.alive? # true

1 Answer

Florian Gross

11/18/2004 12:46:00 AM

Hal Fulton wrote:

> NOTES:
>
> [...]
> - you don't have to pass in the class name
> - it doesn't go into the Struct:: namespace

Note that you don't have to for Struct.new either. It can be used like this:

Person = Struct.new(:name, :age, ...)

Pretty interesting approach by the way.

comp.lang.ruby

[ANN] SuperStruct

Hal E. Fulton

Florian Gross

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