Dynamic linking for SPM

[npvisual]

Added .dynamic in the products definition to make sure the SPM bundle is dynamically linked.

[npvisual]

See #265 for more information about the rational behind this PR.

[srdanrasic]

How about we keep ReactiveKit static and add ReactiveKitDynamic product as an alternative option? I would like to keep the default one static since I think that's the most common use case.

[npvisual]

Sure thing. See the new commit. We could explicitly declare ReactiveKit as .static if you prefer.

[npvisual]

All 3 options could be offered :

    products: [
        .library(name: "ReactiveKit", targets: ["ReactiveKit"])
        .library(name: "ReactiveKitStatic", type: .static, targets: ["ReactiveKit"])
        .library(name: "ReactiveKitDynamic", type: .dynamic, targets: ["ReactiveKit"])

[srdanrasic]

Do you think it would make sense to offer all three options? We could do that.

[npvisual]

The only reason I can think of is if we'd want more control down the road when Xcode can "magically" decide how to link those libraries inside frameworks and it doesn't really work as intended or there's no option to "force" one behavior or the other.

[srdanrasic]

Forward thinking, sounds good to me :) Let's do all three options then. I'll release a new versions when you have the updated PR.

[npvisual]

FYI. Still working through the kinks... Adding 2 libraries seem to be creating some issues. Trying to fix that.

[npvisual]

Ok, after several tests, it seems that the main issue would be wrt Bond's dependencies.

So for example, if we implement the following strategy for Bond :

// swift-tools-version:5.0
import PackageDescription

let package = Package(
    name: "Bond",
    platforms: [
        .macOS(.v10_11), .iOS(.v9), .tvOS(.v9)
    ],
    products: [
        .library(name: "BondDynamic", type: .dynamic, targets: ["Bond"]),
        .library(name: "Bond", targets: ["Bond"])
    ],
    dependencies: [
        .package(url: "https://github.com/npvisual/ReactiveKit.git", .branch("fix/spm-dynamic")),
        .package(url: "https://github.com/tonyarnold/Differ.git", .upToNextMajor(from: "1.4.3"))
    ],
    targets: [
        .target(name: "BNDProtocolProxyBase"),
        .target(name: "Bond", dependencies: ["BNDProtocolProxyBase", "ReactiveKitDynamic", "Differ"]),
        .testTarget(name: "BondTests", dependencies: ["Bond", "ReactiveKit"])
    ]
)

Then the dependencies, for the target, point to :

• either the dynamically linked RK library (as shown above),
• or the statically linked RK library ("ReactiveKit" or "ReactiveKitStatic").

There's a way to impose conditions on target dependencies, but it's limited to platforms at the moment. I am just not sure if it matters, and if we can just use RK's dynamically-linked library and let SPM decide how it's gonna work when Bond is imported into an app.

[npvisual]

@srdanrasic : Here's the Bond Package.swift that I used to validate the changes (compiles and doesn't crash as long as both ReactiveKitDynamic and BondDynamic are used for the dependencies).

https://github.com/npvisual/Bond/blob/fix/spm-dynamic/Package.swift