"""
    power(a, b)

Generic `power`.
"""
function power(a, b)
    a^b
end

"""
    power(a::Integer, b::Integer)

Special case for `power` handling of Integers.
"""
function power(a::Integer, b::Integer)
    # special sauce here
    a^b::Integer  # type isn't required here as it is inferred
end

power

?power

search: power powermod

power(a, b)

power(a::Integer, b::Integer)

struct MyMeasurement
    val::Float64
    err::Float64
end
Base.:*(m::MyMeasurement, other::Number) = MyMeasurement(m.val * other, m.err * other)
MyMeasurement(1.0, 0.1) * 2.0

MyMeasurement(2.0, 0.2)

methods(*)

KERNEL EXCEPTION
BoundsError: attempt to access 208-codeunit String at index [1:211]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 208-codeunit String at index [1:211]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 208-codeunit String at index [1:211]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 209-codeunit String at index [1:212]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 209-codeunit String at index [1:212]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 209-codeunit String at index [1:212]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 209-codeunit String at index [1:212]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 209-codeunit String at index [1:212]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 209-codeunit String at index [1:212]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

KERNEL EXCEPTION
BoundsError: attempt to access 209-codeunit String at index [1:212]

Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] getindex(s::String, r::UnitRange{Int64})
   @ Base ./strings/string.jl:276
 [3] complete_request(socket::ZMQ.Socket, msg::IJulia.Msg)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/handlers.jl:115
 [4] #invokelatest#2
   @ ./essentials.jl:819 [inlined]
 [5] invokelatest
   @ ./essentials.jl:816 [inlined]
 [6] eventloop(socket::ZMQ.Socket)
   @ IJulia ~/.julia/packages/IJulia/Vo51o/src/eventloop.jl:8
 [7] (::IJulia.var"#15#18")()
   @ IJulia ./task.jl:514

ccall(:clock, Int32, ())

19550882

# use actual example
using Statistics
values = [1,2,3,4,5]
√(sum((values .- mean(values)).^2) / (length(values) - 1))

println(π * 1.0)

🎲() = rand(1:6)  # you can go too far... 😜
🎲()
ρ = 1.0

3.141592653589793

1.0

# Euler–Riemann zeta function
function ζ()
    total = 0.0
    for k = 1:100_000_000
        total += 1.0/(k*k)
    end
    sqrt(total*6)
end
@time @info ζ()  # note that you want to precompile functions and you need a proper benchmark, please use BenchmarkTools

# For completeness, the vectorized notation
function ζv()
    a = 1:100_000_000
    total = sum(1 ./ (a.*a))
    sqrt(total*6)
end
@time @info ζv()

a = [1,2,3]

  0.183470 seconds (138.19 k allocations: 9.657 MiB, 31.07% compilation time: 87% of which was recompilation)

[ Info: 3.14159264498239

  0.108846 seconds (355 allocations: 762.969 MiB, 5.41% gc time)

[ Info: 3.1415926440404984

3-element Vector{Int64}:
 1
 2
 3

@code_warntype ζ()

MethodInstance for ζ()
  from ζ() @ Main In[7]:2
Arguments
  #self#::Core.Const(ζ)
Locals
  @_2::Union{Nothing, Tuple{Int64, Int64}}
  total::Float64
  k::Int64
Body::Float64
1 ─       (total = 0.0)
│   %2  = (1:100000000)::Core.Const(1:100000000)
│         (@_2 = Base.iterate(%2))
│   %4  = (@_2::Core.Const((1, 1)) === nothing)::Core.Const(false)
│   %5  = Base.not_int(%4)::Core.Const(true)
└──       goto #4 if not %5
2 ┄ %7  = @_2::Tuple{Int64, Int64}
│         (k = Core.getfield(%7, 1))
│   %9  = Core.getfield(%7, 2)::Int64
│   %10 = total::Float64
│   %11 = (k * k)::Int64
│   %12 = (1.0 / %11)::Float64
│         (total = %10 + %12)
│         (@_2 = Base.iterate(%2, %9))
│   %15 = (@_2 === nothing)::Bool
│   %16 = Base.not_int(%15)::Bool
└──       goto #4 if not %16
3 ─       goto #2
4 ┄ %19 = (total * 6)::Float64
│   %20 = Main.sqrt(%19)::Float64
└──       return %20

A = rand(5)  # random
B = ones(5,2,3)  # 5x2x3 array of 1s
C = Matrix(undef, 5, 5)  # initialize without (re)setting memory values

[1,2,3,4,5] .* [1,2,3,4,5]

5-element Vector{Int64}:
  1
  4
  9
 16
 25

# Everything's a string first
prog = "1 + 1"
ex1 = Meta.parse(prog)
println("$(typeof(ex1)) $ex1")

# An expression has a head and args
println(ex1.head)
println(ex1.args)

# You can create this yourself as well
ex2 = Expr(:call, :+, 1, 1)
ex2 == ex1

Expr 1 + 1
call
Any[:+, 1, 1]

true

]?

  Welcome to the Pkg REPL-mode. To return to the julia> prompt, either press
  backspace when the input line is empty or press Ctrl+C.

  Full documentation available at https://pkgdocs.julialang.org/

  Synopsis

  pkg> cmd [opts] [args]

  Multiple commands can be given on the same line by interleaving a ; between
  the commands. Some commands have an alias, indicated below.

  Commands

  activate: set the primary environment the package manager manipulates

  add: add packages to project

  build: run the build script for packages

  compat: edit compat entries in the current Project and re-resolve

  develop, dev: clone the full package repo locally for development

  free: undoes a pin, develop, or stops tracking a repo

  gc: garbage collect packages not used for a significant time

  generate: generate files for a new project

  help, ?: show this message

  instantiate: downloads all the dependencies for the project

  pin: pins the version of packages

  precompile: precompile all the project dependencies

  redo: redo the latest change to the active project

  remove, rm: remove packages from project or manifest

  resolve: resolves to update the manifest from changes in dependencies of
  developed packages

  status, st: summarize contents of and changes to environment

  test: run tests for packages

  undo: undo the latest change to the active project

  update, up: update packages in manifest

  why: shows why a package is in the manifest

  registry add: add package registries

  registry remove, rm: remove package registries

  registry status, st: information about installed registries

  registry update, up: update package registries

# please write your function here. Shift enter or the play button above executes it
x = "hello world"
x

"hello world"

Introduction: What is Julia¶

Solving the two language problem¶

Features (the good)¶

Multiple dispatch¶

Interopability¶

Unicode¶

Performance¶

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Package manager¶

When to use¶

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Exercise¶

The community¶