Forums

Making StreamReader Iterable

General discussion about Cobra. Releases and general news will also be posted here.
Feel free to ask questions or just say "Hello".

Making StreamReader Iterable

Postby oahmad04 » Sun Jan 26, 2014 8:44 pm

I tried to make StreamReader iterable with the following:
extend StreamReader
"""Makes StreamReader iterable (by line)"""

cue enumerate as String*
"""Yields each line in the open file"""

test

# Make and test a file:

File.writeAllText("Source", "line 1\nline 2\nline 3")
lines = []

using file = File.openText("Source")
for line in file, lines.append(line)

assert lines == ["line 1\n", "line 2\n", "line 3"]

File.delete("Source")

# Make and test an empty file:

File.writeAllText("Source", "")
lines = []

using file = File.openText("Source")
for line in file, lines.append(line)

assert lines == []

File.delete("Source")

body

while true
line = .readLine
if line is nil, break
yield line to !

I get the following errors:

Code: Select all
iterateFile.cobra(23): error: Cannot infer the type for "line" from the "for" loop.
iterateFile.cobra(35): error: Cannot infer the type for "line" from the "for" loop.


What did I do wrong? Thanks.
oahmad04
 
Posts: 19

Re: Making StreamReader Iterable

Postby Charles » Sun Jan 26, 2014 9:01 pm

Part of being enumerable to a "for" loop is implementing IEnumerable. You cannot make this happen to an existing class (by using extend or any other technique).

Note that .NET 4 introduced File.readLines which basically does what you're looking for:
http://msdn.microsoft.com/en-us/library ... 3(v=vs.110).aspx

If you still wanted to put something on a reader, and you don't mind slapping a method on the reader in the for loop, then you could do something like this:

extend TextReader

def readLines as String*
...

...

for line in tr.readLines, print line

Note that other possibilities for looping through a reader include characters, words and regex matches. For this reason, I would actually prefer this form over making the reader directly enumerable.
Charles
 
Posts: 2515
Location: Los Angeles, CA

Re: Making StreamReader Iterable

Postby Charles » Sun Jan 26, 2014 9:02 pm

Also, in Cobra tests, it is customary to use StringWriter and StringReader in place of actual file I/O. The tests will run faster, have less side effects on the machine and less of a chance of failing for external reasons (permissions, etc.).
Charles
 
Posts: 2515
Location: Los Angeles, CA

Re: Making StreamReader Iterable

Postby oahmad04 » Sun Jan 26, 2014 10:00 pm

Thanks for your response. I thought it would be like Python where you just add a "def __iter__" method and it works. Now I know.

Charles wrote:Note that other possibilities for looping through a reader include characters, words and regex matches. For this reason, I would actually prefer this form over making the reader directly enumerable.


Good point. I was missing the Python syntax. I should probably just use what's given with Cobra instead of trying to make working with files more like Python.

Charles wrote:Note that .NET 4 introduced File.readLines which basically does what you're looking for:
http://msdn.microsoft.com/en-us/library ... 3(v=vs.110).aspx


I saw this actually. Very handy. I was just worried it wouldn't work with huge files. I don't actually have any huge files in mind. I'm not working on any projects. I'm just learning Cobra by making little namespaces I think will be useful.
oahmad04
 
Posts: 19

Re: Making StreamReader Iterable

Postby oahmad04 » Sun Jan 26, 2014 10:06 pm

I saw this actually. Very handy. I was just worried it wouldn't work with huge files. I don't actually have any huge files in mind. I'm not working on any projects. I'm just learning Cobra by making little namespaces I think will be useful.

Oh, I haven't seen this. I thought you posted a link to readAllLines. This is cool.
oahmad04
 
Posts: 19


Return to Discussion

Who is online

Users browsing this forum: No registered users and 6 guests

cron