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Interfaces
A new leaf in an old book
Matthew Cottingham
[email protected]
@mattrco
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whoami
Then: web services,
ETLs, messaging.
Now: forum software,
web services all Go
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–Russ Cox
“Go's interfaces… are, for me, the
most exciting part of Go from a
language design point of view.”
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Recap
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Stringer
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Implicitly satisfied interfaces
• In order to satisfy an interface, we just need to
implement the right functions
• So it’s easy decouple components even if they’re
third party or part of the standard library
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Decoupling database/sql
• sql.DB is a struct type which makes it harder to
switch out for a test implementation
• Create an interface type (I called it DBer) with
same methodset as sql.DB
• Replace instances of sql.DB with interface DBer
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DBer interface type
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DBer usage
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Other options
• https://github.com/erikstmartin/go-testdb
• also, fakedb (internal test package) implements
the Driver interface
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Real-world interfaces
• There are some useful examples of interfaces in
the standard library:
• encoding for text and binary representations
• Valuer and Scanner interfaces
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encoding interface
• New in Go 1.2
• Supports Binary and Text Marshal/Unmarshal
• Used in e.g. Time and IP types
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(Un)MarshalText
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net.IP implementation
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Valuer and Scanner
• Database driver needs to convert Go types to
database types and vice-versa
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PostgreSQL hstore
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Analysis
• go oracle can tell you (among other things)
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References
• http://research.swtch.com/interfaces
• http://blog.golang.org/gif-decoder-exercise-in-go-
interfaces
• http://jmoiron.net/blog/built-in-interfaces/
• Source code modified from:
• http://golang.org
• https://github.com/lib/pq